Slippers

Abstract

Elastomeric slippers, having an upper blank joined to a lower blank to form a bottom sole and at least a front-of-the-foot cavity, exhibit improved tear resistance by the formation of the marginal rear edge of the upper blank in such a way as to form an acute angle with the coextensive marginal edge of the lower blank. Additional tear resistance is added when the marginal rear edge is formed as a forwardly extending cusp so as to circumvent the upper half of the foot's instep.

Description

This invention relates to slippers formed from elastomeric material and having improved tear resistance. More particularly, this invention relates to slippers of either the heel-binding or scuff type which exhibit improved tear resistance at the point of rear-most intersection between the upper and lower blank.

Heretofore there has been a need for strong, sanitary and inexpensive footwear and for efficient methods of manufacturing such footwear. This need has been met to a substantial extent by the footwear and production methods disclosed in our U.S. Pat. No. 3,238,079. Plastic slippers fabricated in accordance with the teachings of that patent are enjoying widespread and steadily increasing commercial use where paper slippers (or none at all) were used previously. Considering the plastic foam sheeting which must be used to permit economical pricing, and the fact that the slippers are held in place on the wearer's foot, in part, by internal elastic tension in the plastic foam material, they display a surprising degree of resistance to tearing while in use.

In our U.S. Pat. No. 3,638,262 there is disclosed a further and somewhat different type of foot-wear and production methods which also fulfill the above described need in the art for strong, sanitary and inexpensive footwear and for efficient methods of manufacturing same. Generally speaking such footwear provide for excellent retention coverage of the wearer's heel, and at the same time the requisite internal tension to keep them in place on the foot when in use. And this is true regardless of whether the slipper is small, medium, or large in size. Such a result is generally achieved by forming the footwear of a sole member (of elastomeric sheet material) wherein there is a toe portion, a heel portion and marginal edges extending from the toe portion to the heel portion; an upper member attached to the toe portion by seams extending generally horizontally along said upper member and said marginal edges; the marginal edges of the sole member tapering upwardly and inwardly at points progressively further from said toe portion; the upwardly and inwardly tapering portions of the sole member defining the left and right sides of the heel portion of the footwear, the upwardly tapering portions of the sole member being joined together at the heel of the footwear in a generally upright seam which is at least partly forwardly inclined.

It has been discovered however that the slippers disclosed in U.S. Pat. No. 3,638,262 are subject to certain periodic failures with actual failure occuring in the lower portion, usually by way of a lateral tear. It has also been found that slippers of a similar type, but formed without a retaining heel portion (i.e. in "scuff" form), also exhibit this same tendency to tear. These periodic failures, although infrequent, are annoying and an inconvenience. They generally originate at the point where the rear edge portion of the upper blank intersects with and is joined to the sole portion along the marginal edges of the upper and the sole. Accordingly, a need remains for improvements in plastic slippers and methods of making them which adequately protect against undesirable failures.

It is a purpose of this invention to fulfill this need and other needs which will be apparent to those skilled in the art from the following description of our footwear and certain embodiments thereof.

SUMMARY OF THE INVENTION

The above-described needs of the art are met by this invention which provides a slipper comprising an upper attached to a sole of lower blank of elastomeric sheet material. The sole may be in scuff form (i.e., without a retaining heel), but in particularly preferred embodiments the marginal edges of the lower blank taper upwardly and inwardly at a point successively closer to the heel similarly as disclosed in U.S. Pat. No. 3,638,262. As further disclosed in this patent, at the heel, the left and right sides of the lower blank join one another in a generally upright seam which is at least partly forwardly inclined for gripping the wearer's heel and thus providing a retaining heel. The entire disclosure of U.S. Pat. No. 3,638,262 is incorporated herein by reference.

The problem of tearing or failure which tends to originate at the rearmost intersection between the upper and lower blank, as described above, and which usually promulgates itself as a lateral tear through the sole, is then solved in accordance with this invention by forming the juncture of the rear of the upper blank with the lower blank such that the terminal or rear edge of the upper approaches the seam between the upper and lower blanks at an acute angle. It has been found that when this is done, a marked reduction in the described tendency to fail is experienced.

Any acute angle will reduce the tendency to fail. However, it is preferred for the purposes of this invention, and particularly when forming the heel-retaining slippers of U.S. Pat. No. 3,638,262, that the angle be no greater than about 80.degree. from the horizontal (i.e., greater than 10.degree. from the vertical) and preferably between about 30.degree. to 60.degree. from the horizontal, thp lower limit being based primarily on the need to provide adequate front-of-the-foot retention.

It has been further found that additional tear resistance can be added to the slippers of this invention if the upper blank circumvents the upper half of the foot's instep during use. Thus in particularly preferred embodiments the acute angle, formed on both sides of the slipper is made to continue in a rear edge of the upper blank so as to form a forwardly extending cusp which, when a foot is present in the slipper, extends around substantially all of the upper portion of the foot's instep, thus further reducing the tendency to tear.

While the slippers of this invention may be formed by any known technique, it is of course, preferred that they be formed by the unique methods of joinder disclosed in U.S. Pat. No. 3,238,079 and of production generally, as disclosed in U.S. Pat. No. 3,638,262. The disclosures of these two patents are incorporated herein by reference. The methods of these patents are readily adapted to forming a "scuff" type slipper merely by omitting (from the production techniques of U.S. Pat. No. 3,638,262) the outwardly diverging feature and forming the heel portion of the sole in a flat heel configuration. The additional step of sealing the heel retaining portion is, then, of course, eliminated.

The acute angle seam and such other seams as may be required (e.g., the heel seam in the heel-retaining embodiment) may be formed by any effective method of joinder, such as sewing, cementing, thermal sealing, induction sealing and the like. Preferably, thermal sealing as disclosed in the aforementioned patents is employed.

As used herein, the term "elastomeric" is intended to include any material, natural, or synthetic, characterized by flexibility and stretchy elasticity, and is preferably, though by no means essentially, spongy. That is, the material preferably includes cellular structure. A preferred example of such a spongy material is open-celled polyurethane foam, a synthetic elastomeric material which may be produced by "blowing" a polyester resin with a diisocyanate compound. Such materials are readily available commerically in sheet form from a number of suppliers and are readily amenable to the various methods of joinder described in U.S. Pat. No. 3,238,079.

Generally speaking, the method which is employed to form the slippers of this invention includes: providing (e.g., by cutting die or the like) a first layer of heat sealable elastomeric material so designed to form an acute angle and also preferably a cusp as described, bringing said first layer and a substantially wider second layer of heat-sealable elastomeric material into face-to-face relationship with one edge of each layer being substantially aligned with one edge of the other to provide in said second layer a covered portion which is in face-to-face relationship with the first layer and an exposed portion which is not in face-to-face relationship with the first layer; in a first bonding operation uniting said layers to form therein the toe portion of a slipper by subjecting the first layer and the covered portion of the second layer to sufficient heat and pressure to form a heat-sealed bond between them in a first narrow region having two branches extending away from substantially aligned edges and spaced apart from one another by approximately the width of the toe and instep of a human foot of predetermined size; while still under the pressure of the said first bonding operation, cutting the material of the first and second layers along the first narrow region; and cutting the exposed portion of the second layer along lines extending from the ends of said branches in a direction away from the aligned edges of the layers to form a blank having its longitudinal axis extending away from the said aligned edges and separating the blank from the remainder of the material of said layers. In those instances where a "scuff" is formed, no further steps are necessary and the "exposed" portion will, of course, form the scuff heel portion. In those preferred instances where a retaining heel is formed, for example in accordance with U.S. Pat. No. 3,638,262, the method further includes: folding the material of the exposed portion of the second layer in the blank on either side of the longitudinal axis thereof into face-to-face relationship in a plane generally perpendicular to the first narrow region; and, in a second bonding operation, forming the heel of a slipper by subjecting the folded exposed portion of the second layer to sufficient heat and pressure to form a heat-sealed bond in a second narrow region which is spaced longitudinally of said blank from said first layer and is in a plane generally perpendicular to said first region.

Although the terms "first layer" and "second layer" may in some contexts connote two separate pieces of material, these terms are used herein not only with that connotation in mind, but also to refer to different portions of the same piece of material which has been folded upon itself to form two or more layers.

"Heat-sealable material" refers to any supple synthetic polymeric web which may be bonded to itself and to other materials by coalescence or melting together under the action of pressure and heat, whether induced thermally or electronically.

The formation of the acute angle (including cusp if so desired) may be accomplished by any known technique such as providing the first layer as a preform. Preferably, however, the first layer is cut to shape the angle as one of the steps in the continuous operation substantially as disclosed in the aforementioned U.S. Pat. No. 3,638,262. This is accomplished by providing a cutting die which cuts a cusp or acute angle from the requisite lateral edge of the first layer at intervals geared to substantially align the angled cut with the second layer prior to heat sealing. This may be done, for example, at the same point in the operation of U.S. Pat. No. 3,638,262 where the folded over portion was provided in the first layer.

When it is stated that edges of the layers, angled cuts or cusp are "substantially aligned" or the like, it is not required that these edges, etc. exactly coincide or even be precisely parallel, although such is definitely preferred from the standpoint of production efficiency and avoiding waste of material; it is sufficient if the edges etc. approximately coincide or be approximately parallel and adjacent to one another.

The "face-to-face relationship" referred to above does not require the layers to contact one another over their entire adjacent surfaces. For instance, the layers may be closely adjacent to one another but separated prior to bonding by a layer of thin, loosely woven cloth or scrim material through which the heat-sealable materials of the respective layers may flow during the bonding operation to form a seal, thus enveloping and bonding the cloth or scrim material in the seal between the layers and enabling it to serve as a liner in the finished slipper. Thus, it is apparent also that the method as stated above comprehends the formation of slippers having two or more layers of one or more different materials. The usual practice however will be to employ a synthetic polymer foam webbing material in a construction which includes just a first and second layer.

The extent to which the second layer is wider than the first is dependent upon how much of the wearer's foot it is desired to have covered by the slipper, and how much waste can be tolerated in the manufacturing process. Generally, the second layer will be about 1.5 to about 5 times as wide as the first layer, measured between the first and second regions.

The two "branches" of the first narrow region refer to those portions of the heat seal between the first and second layers which extend respectively along the right and left sides of the toe portion of the slipper. These branches may meet in the manner of the arms of a "V" if a pointed toe is desired or may meet in the manner of the arms of a "LL" or any other suitable manner.

The aforesaid first and second regions may be continuous or discontinuous, as it is known to produce heat seals which are continuous or which are closely adjacent increments of sealed material longitudinally interspersed with unsealed or only partially sealed material. When the first and second layers are of different colors, this provides a varicolored seal of pleasing appearance.

Although the cutting of the blank should take place while the first region is still under the pressure of the bonding operation, this should not be construed as requiring that the bond should be complete at the time cutting takes place. The cutting may occur before, during or after formation of the bond. The term "cutting" is intended to be construed broadly to cover cutting, shearing, tearing and generally any other suitable mode of separating the blank from the remaining portions (e.g., waste) of the first and second layers. The cutting "along the first narrow region" may be performed along the outer edge of the region, or even within the region, in which event part of the seam remains with the blank and the remainder goes with the waste. This cutting operation is best -- though not essentially -- performed simultaneously with the cutting of the exposed portion of the second layer to complete the cutting of the blank in one operation.

The lines along which the exposed portion is cut preferably diverge from one another as they extend away from the toe portion so as to provide for a heel retaining portion. Experiments have shown that the lines may converge some, but as the angle of convergence increases, the height and therefore the gripping capabilities of the heel are reduced. Therefore, it is preferred that the angle between the aforesaid lines be in the range of about 0.degree. to about 90.degree..

This invention will now be described with reference to certain embodiments in conbination with accompanying illustrations of which:

IN THE DRAWINGS

FIG. 1 is a side elevation (nonwearing position) of a slipper as disclosed in U.S. Pat. No. 3,638,262.

FIGS. 2 and 3 are perspective (wearing position) and top plan (nonwearing position) views of the aforementioned prior art slipper.

FIGS. 4 and 5 are side and rear elevations (nonwearing position) of a novel slipper corresponding with the present invention.

FIGS. 6 and 7 are perspective (wearing position) and top plan (nonwearing position) views of the aforementioned slippers of the present invention.

FIGS. 8 and 9 are perspective (wearing position) and top plan (nonwearing position) views of a "scuff" type slipper in accordance with this invention.

An illustrative embodiment of the prior art slipper of U.S. Pat. No. 3,638,262 shown in FIGS. 1-3 includes an upper blank 20 having a folded-over portion 21 at its rear edge 22.

The sole or lower blank 23 is joined to the upper along a seam of fused materal 24 such as is formed by a thermal heat-sealing and cutting procedure and apparatus of the type hereinafter described. For convenient description the lower blank is referred to hereinafter as having a toe or covered portion 26 -- which is that portion which coincides with and is covered by the upper and a rear or exposed portion 27 -- which includes all of the lower blank to the rear of rear edge 22 of the upper. The toe portion of the lower blank and the upper are generally horizontally disposed and have a width and a shape which are generally conformable to those of a human foot, but the shape may be varied freely in accordance with the dictates of convenience and fashion. When the upper is provided with a folded over portion 21, it is beneficial to have that portion joined to the remainder of the upper and to the lower in seam 24 as shown in FIGS. 1-3. In any event, the rear edge 22 of the upper extends from one lateral edge 28 to the other lateral edge 29 of the lower blank and is free of attachment to said blank except at said lateral edges, thereby providing a sort of pocket for insertion of the wearer's toes, which pocket may be open, closed, rounded flat or pointed at the toes as desired. The longitudinal position of rear edge 22 may be moved forward or backward as desired so long as adequate room for insertion of the wearer's foot and satisfactory coverage of the toes are provided.

There is, in the rear portion of blank 23, a tapering inwardly and upwardly of the lateral edges 28 and 29 toward a vertical plane 30 (FIG. 3) which passes through the slipper about at its longitudinal axis. The material of the exposed portion of the lower bends upward as it passes through this plane with the radius of curvature in the bend generally increasing (while the slipper is not being worn) at points along the axis successively closer to the heel. At the extreme rear of the exposed portion the left 33 and the right 34 sides of the lower blank join and are bonded with one another along a heel seam 31. A portion 32 of this seam is inclined forwardly to grip the wearer's heel. The remainder of the seam may incline backwardly or forwardly to provide a smooth-fitting heel or various decorative effects. Preferably, the heel seam 31 is in the form of a smooth curve which, at its lower end, lies approximately tangent to the bottom of the lower blank, and at its upper end, intersects the marginal edges 28 and 29 at an acute angle, said angle being measured with the slipper folded along its longitudinal axis with the inner surfaces of sides 33 and 34 in face-to-face contact.

FIGS. 1-3 further illustrate the type of failure which may occur in these slippers, either of the heel retaining or scuff type. As stated above, during use there is a tendency for these slippers to fail by the origination of a tear B at point A which as illustrated usually promulgates itself laterally across sole blank 23 until the slipper parts into two pieces.

FIGS. 4-7 illustrate a particularly preferred embodiment of this invention in that it incorporates the beneficial heel-retention benefits of the slippers of FIGS. 1-3 and, at the same time, reduces the occurance of failure. As shown, the slipper includes an upper blank or portion 50 having a specifically designed rear edge 52. The rear edge may be provided with a folded over portion as shown in FIGS. 1-3. On the other hand, the folded over portion may be omitted, as it is in FIGS. 4-7, to provide for ease of manufacturing. The rear edge 52 may have various decorative outlines. However, in all cases the rear edge 52 should approach the seam of fused material 54 forming the toe portion of the slipper at an acute angle as discussed in greater detail below. This feature as discussed above is believed to be of primary importance in overcoming the periodic failures (as illustrated in FIGS. 1-3) of the slippers at that point.

The sole or lower blank 53 is joined to the upper along a seam of fused material 54 such as is formed by a thermal heat-sealing and cutting procedure. For convenient description, the lower blank is referred to hereinafter as having a toe or covered portion 56 -- which is that portion which coincides with and is covered by the upper -- and a rear or exposed portion 57 -- which includes all of the lower blank to the rear of rear edge 52 of the upper. The toe portion of the lower blank, and the upper are generally horizontally disposed and have a width and a shape which are generally conformable to those of a human foot, but the shape may be varied freely in accordance with the dictates of convenience and fashion as is the case with the prior art slipper. The rear edge 52 of the upper extends from one lateral edge 58 to the other lateral edge 59 of the lower blank and is free of attachment to said blank except at said lateral edges, thereby providing a sort of pocket for insertion of the wearer's toes, which pocket may be opened, closed, rounded, flat or pointed at the toes as desired. The longitudinal position of rear edge 52 may be moved forward or backward as desired so long as adequate room for insertion of the wearer's foot and satisfactory coverage of the toes are provided.

It is a primary feature of the present invention that there be a specific arrangement by which the rear edge 52 of the upper 50 meets or approaches the aforementioned seam 54 of fused material. As the terminal ends of the rear edge 52 approach point A, they should do so in such a manner as to form an acute angle .alpha. with the seam 54. The size of the angle is not particularly critical to the present invention as long as the angle is acute (or less than 90.degree.). Preferably the angle .alpha. is less than about 80.degree. and more preferably from about 30.degree. to about 60.degree.. As discussed above, it has been found that when the ends of the rear edge 52 approach the seam of fused material 54 forming an acute angle according to the present invention, the periodic failures of the slippers of the prior art at point A are drastically reduced. Thus, a greatly improved elastomeric slipper is formed in accordance with the present invention.

Of course, the interior portion of the rear edge 52 may have various decorative outlines, such as wavy, curved, or serrated, as long as the end portions of the rear edge approach seam 54 so as to form an acute angle as discussed above and as further discussed above, it has also been found that failure at point A can be further averted if edge 52 forms a forwardly extending, substantially circular cusp which circumvents the upper portion of a foot's instep when inserted in the slipper.

The reason for the reduction of failures obtained when following the teachings of the present invention are not definitely known. It is believed, however, that one of the major causes of failure was due to the folded over top layer which stretched less than the single bottom layer to which it was sealed. Thus, when the foot was flexed during use so as to stretch the slipper, the upper layer stretched less (i.e., resisted more) than the lower layer, putting a non-uniform stress at point A. On the other hand, this was not the only cause of failure since slippers having single layered uppers also failed in the same way. It is further believed, therefore, that regardless of the type layers employed, point A (or thereabouts) constitutes a maximum pressure or stress point in the slipper structure when in use.

It was then found that when the ends of rear edge 52 approach the seam 54 at an acute angle .alpha., the point of greatest pressure is dispersed, thus reducing the chance of failure. And this is true whether a single or double layered upper is employed -- it being preferred of course to employ only a single (i.e., unfolded) layer.

It is also believed that by providing a cusp or other arrangement (design) so as to circumvent the upper instep of the foot, pressure on seam 54 during movement of the foot (e.g., during walking) is reduced, thus further reducing the occurance of periodic failures.

In accordance with a preferred embodiment of the invention, the lower blank 53 has a rearwardly divergent width; that is, the width of the material in the blank, measured flat, increases when measured perpendicular to the longitudinal axis of the slipper at a plurality of points successively closer to the heel. Such divergency may exit only in the exposed portion of the lower or in both the exposed portion and covered portion, the latter being the preferred mode which is disclosed herein. The angle of divergence, measured between the marginal edges of the flattened lower blank, should be substantial, e.g., at least about 10.degree.. Angles of divergence of about 10.degree. to about 45.degree. are preferred, with an angle of about 18.degree. - 20.degree. being considered best. Larger angles can be used, but the amount of waste material produced in the making of the slippers increases as the angle is increased. Thus, when we state that the contemplated range of the angle of divergence is from about 10.degree. to about 90.degree., there is no intention of ruling out larger angles. "About 90.degree." is recited merely as the angle beyond which the economic penalty associated with widening the angle of divergence is believed sufficiently great as to make any further increase undesirable from the standpoint of efficient manufacturing practice.

It is another feature of this invention that there is provided, in the rear portion of blank 53, a tapering inwardly and upwardly of the lateral edges 58 and 59 toward a vertical plane 60 (FIG. 5) which passes through the slipper about at its longitudinal axis. The material of the exposed portion of the lower bends upward as it passes through this plane with the radius of curvature in the bend gradually increasing (while the slipper is not being worn) at points along the axis successively closer to the heel. At the extreme rear of the exposed portion the left 63 and right 64 sides of the lower blank join and are bonded with one another along a heel seam 61. A portion 62 of this seam is inclined forwardly to grip the wearer's heel. The remainder of the seam may incline backwardly or forwardly to provide a smooth-fitting heel or various decorative effects. Preferably, the heel seam 61 is in the form of a smooth curve which, at its lower end, lies approximately tangent to the bottom of the lower blank, and at its upper end, intersects the marginal edges 58 and 59 at an acute angle, said angle being measured with the slipper folded along its longitudinal axis with the inner surfaces of sides 63 and 64 in face-to-face contact.

The slipper of the herein disclosed preferred embodiment is further characterized in that the lower blank 53 extends as a single, continuous layer of elastomer foam material from one marginal edge to the other, so that one and the same piece of material serves as the sole, sides and heel of the slipper. Because said layer is preferably formed into a heel portion by a generally upright angle seam which unites the material on the left side of the longitudinal axis of the slipper to that on the right, the sides and rear of the slipper can be formed from the folded blank in a single operation without the necessity of any horizontal seaming, as is required in most conventional shoe, slipper and mocassin configurations.

In a commercial embodiment of the herein described slipper, the radius of curvature of the leading edge of the toe portion is about 2 inches. The angle of divergence of the lateral marginal edges of the upper and lower, measured with the lower blank flattened against a planar surface is about 18.degree. - 20.degree.. The upper, measured from the front to the rear edge at the longest point, is about 5 inches long. The width of the upper, measured along its rear edge is about 51/4 inches. The overall length of the slipper, measured along its longitudinal axis is about 12 inches. The radius of curvature of the heel seam is about 41/2 inches. The angle .alpha. is about 45.degree. and the radius of the curvautre of the cusp is sufficient such that if viewed from the top, in flat perspective, the cusp would form a substantial tangent with the line of seam 54 as best illustrated in FIG. 7. In actual production and to insure efficiency and proper alignment on a mass production basis, the arc of the cusp is generally made to extend somewhat beyond the intersection (e.g., about one-half inch on either side) thus forming a line at the point of intersection which is just short of being a tangent. Such a cusp then extends forward at maximum depth of about 1 - 2 inches which is sufficient to insure circumvention of the upper instep of the foot.

FIGS. 8-9 illustrate a "scuff" type of slipper formed in accordance with this invention. As illustrated the slipper is simply formed of an upper blank 72 which is sealed at 74 to lower or sole blank 76. In keeping with the unique discovery of this invention rear edge 78 forms an acute angle .alpha., preferably within the same range of acuteness as hereinbefore described, with sole 76 at point A. Also in keeping with the further unique discovery of this invention, cusp 80 of upper 72 has a radius R sufficient to substantially circumvent, and thus not override the upper instep of a foot inserted therein. As illustrated cusp 80 is preferably a semicircle forming a substantial tangent at points A (i.e., just short of being a tangent).

As stated hereinabove the slippers of this invention, as exemplified by FIGS. 4-9, may be formed by any technique known to the art. As further stated and generally outlined above, it is preferred to employ the techniques of the aforementioned two patents since such techniques are economical and form high quality products. It is also preferred for the purposes of this invention to employ the equipment disclosed in these patents when using the methods thereof. It is of course understood that when forming the scuff type slipper illustrated in FIGS. 8-9 the sole blank may be a flat, substantially non-divergent semi-rigid blank so that no "pocket" is formed by upraised walls of the sole blank. In other types of scuffs however, such a feature can be built into the slipper by designing the lower blank properly. For example, if the foot cavity is designed small and flexible enough and the sole blank is slightly wider at the foot cavity than at the heel portion, sole blank will tend to pull up and around the foot when it is inserted therein. Such, of course, adds elastomeric retention pressure to the slipper design.

Once given the above disclosure, many other features, modifications and improvements will become apparent to the skilled artisan. Such other features, modifications and improvements are the efoer considered to be a part of this invention, the scope of which is to be determined by the following claims.

Claims

We claim:

1. In a slipper comprising a first piece of foamed flexible synthetic elastomeric material forming an upper having a front and side outline approximating that of the front portion of a human foot, and terminating in a rear edge, said upper being fusingly joined along its front and side edges to a second piece of foamed flexible synthetic elastomeric material constituting a lower which, to the extent that it coincides with the upper, is of similar shape and of generally planar configuration, said lower transitioning rearwardly of the upper to form a heel portion, said lower having a tendency during use to form a lateral tear through said lower which tear originates at a point approximately where the terminal or end portions of said rear edge of said upper are fusingly joined with said lower, the improvement comprising the upper being formed in such a manner that said rear edge approaches its joinder point with said lower at an acute angle of less than about 80.degree. from the horizontal, whereby said tendency to form a lateral tear through said lower is substantially reduced.

2. A slipper according to claim 1 wherein said rear edge forms a forwardly extending cusp of sufficient size such that when a foot is inserted in the slipper the rear edge circumvents the upper instep of said foot.

3. A slipper according to claim 1 wherein said acute angle is between about 30.degree.-60.degree. from the horizontal.

4. A slipper according to claim 1 wherein said lower transitions rearwardly of the upper to a configuration at the heel in which the edges of the lower are directed upwardly to form side portions of the heel of said slipper, said side portions joining one another at said heel in a generally upright, forwardly inclined seam.

5. A slipper in accordance with claim 4 wherein said acute angle is from about 30.degree. to about 60.degree..

6. A slipper in accordance with claim 4 wherein said seam is forwardly inclined for gripping the wearer's heel, said upper edges and seam are disposed at an acute angle to one another at their point of intersection, and said intersection is adjacent to the wearer's heel.

7. A slipper in accordance with claim 6 wherein said seam is a heat-seal.

8. A slipper according to claim 4 wherein said rear edge of said upper forms a forwardly extending cusp of sufficient size such that when a foot is inserted in the slipper the rear edge circumvents the upper instep of said foot.