A knit sock, especially for jogging or other athletic activity, has a foot portion which includes an inner ply having a first inner surface formed to make relatively high frictional contact with the skin of the wearer and a second, outer surface having relatively low frictional characteristics. The inner ply is inserted within and fixed to an outer ply which includes a first inner surface having relatively low frictional characteristics disposed adjacent said second surface of said first ply and a second, outer surface having a relatively high frictional surface adapted to make contact with the interior of a shoe.

BACKGROUND OF THE INVENTION 
A. Field of the Invention 
This invention relates to socks in general and in particular to a two-ply 
sock of improved internal antifriction construction for athletic activity 
such as jogging. 
B. Prior Art 
Since the advent of the jogging craze, there has been an ever increasing 
emphasis upon the comfort of the jogger by designing improved shoes and 
socks which are intended to reduce the physical toll on the feet and legs 
of the jogger or to increase his foot comfort. Toward this end, various 
types of sock conceptions have been patented or sold which purport to 
offer superior comfort, greater foot-ease, greater shock-absorbency, and 
other advantages. 
U.S. Pat. No. 3,250,095 to Bird teaches a single ply sock with inside terry 
loops of hydrophilic yarn and outside hydrophobic and elastic yarn. The 
avowed purpose of this construction is to hold or carry perspiration away 
from the skin of the wearer, but still provide good thermal insulating 
qualities by providing inside terry loops. Bird asserts that this prevents 
the yarns from matting or packing down during use which thereby destroys 
the thermal insulating and softness characteristics of conventional socks. 
U.S. Pat. No. 3,796,067 issued to East is a two-ply sock with terry loops 
on both the inner and outer surfaces for comfort, warmth and durability. 
Other double-ply athletic socks are avaialble commercially, but they are 
bulky and tend to bunch causing abrasion, blisters and other discomfort. 
Another jogging sock is made of pure silk in two layers, but silk is quite 
costly, much less durable then synthetic fabrics, and difficult to 
launder. Also, the low-frictional characteristics of silk permits the 
inner layer to slide down on the foot of the wearer. 
Another sock is made of pima cotton which also is not very durable. 
Still other single ply and double ply sock constructions have been marketed 
for athletic or jogging use, but they have failed to attain the objects 
that are accomplished by the present invention. 
All known commercially available socks for athletic use are not specially 
constructed to minimize the possibility of blisters. Blisters are caused 
by the abrasive action caused by the rubbing pressure exerted between the 
skin of the foot and adjacent sock surfaces. In the act of running, the 
shoe, sock, and foot are, while the foot is off the ground, in 
substantially identical forward motion. However, when the shoe strikes the 
ground, the shoe tends to undergo an abrupt decrease in velocity whereas 
the foot and sock within the shoe tend to continue forward at a rapid 
speed until the shoe limits the forward motion. Consequently, there is an 
abrasive action which occurs at the interface of the foot and sock and at 
the interface of the sock and shoe. The abrasion and frictional heat built 
up at that interface is the main cause of blisters or irritation. 
It is therefore among the objects of the present invention to provide: 
1. An athletic sock which helps to reduce the occurrence of blisters. 
2. An athletic sock which gives the wearer a feeling of great foot ease. 
3. An athletic sock in which relative motion between the sock and the foot 
is reduced. 
4. An athletic sock wherein relative movement of the foot within the sock 
does not produce bunching of the sock material. 
SUMMARY OF THE INVENTION 
A double-ply sock whose inner ply has one surface formed with high friction 
characteristics adapted to be placed next to the foot and the other 
surface formed with low friction characteristics. The outer ply is fixed 
to the inner ply and has an inner surface formed to have low friction 
characteristics and an outer surface formed to have high friction 
characteristics.

DETAILED DESCRIPTION OF THE DRAWINGS 
FIG. 1 shows a sock in accordance with the present invention which consists 
of an upper cuff portion 12, a leg portion 14 and a foot portion indicated 
generally at 16. In one preferred embodiment, it has an outer ply 18 
inside of, and to which a slightly smaller inner ply 20 is fixedly 
disposed as seen in more detail in FIG. 2. The cuff 12 and leg portions 14 
are not of primary interest; it is the foot portion 16 which embodies the 
essence of the present invention. 
The inner surface 20a of ply 20 is made to have a relatively high friction 
characteristic so that when the foot of the wearer is placed within it, it 
will tend to resist movement or slippage of the sock down the leg of the 
wearer and hence to resist "bunching". The outer surface 20b of the inner 
ply 20 is made to have a smooth, relatively low friction characteristic. 
There is also an outer ply 18 whose inner surface 18a is also made to have 
a low friction characteristic so that when it comes into contact with the 
surface 20b, there will be easy sliding movement between those two 
surfaces. The lower part 18c of the outer ply 18 has terry loops so that 
it will have a relatively high friction characteristic. Thus, when it 
makes contact with the interior of the shoe, it will resist movement of 
the outer layer relative thereto. Since the inner layer 20 is in high 
frictional contact with the foot and the outer layer 18 is in high 
frictional contact with the interior of the shoe, the outer layer will 
tend to remain relatively motionless when the foot of the runner comes to 
a sudden stop as it hits the ground, whereas the inner layer will continue 
forward and slide on the outer layer lessening the abrasive effects of the 
inner layer on the skin surface. 
The material of the inner play may be a composite fabric whose inner 
surface is made of 150 denier unworsted wool yarns and whose outer surface 
consists of a texturized polypropylene yarn plated on the opposite side of 
the inner surface which possesses the desired low friction characteristics 
relative to the wool yarn. 
The material of the outer ply could be a composite fabric whose outer 
surface could be cotton and whose inner surface could also be a texturized 
polypropylene yarn, one material being plated on the other, for example. 
Terry loops of cotton could be formed in the areas 18c of the sock. 
In the manufacture of the sock and, in particular, the choice of yarns for 
the first and second layers resort may profitbly be had to "Cover Spun" or 
"Wonder Spun" yarns such as those made and marketed by Leesona and sold by 
Martin Processing Co. of Martinsburg, Va. These yarns comprise drafted 
rovings of staple fibers such as cotton, rayon or acrylics, polyesters or 
blends of them with a spiral wrapping of continuous monofilament or 
multifilament synthetic fibers such as Nylon 6 or 66, polyester, 
polypropylene, etc. The inner yarns comprise essentially untwisted 
parallel fibers bound together by the spiral wrapping. 
For the inner layer of the sock, nylon wrapped around cotton or rayon yarns 
of the "Cover Spun" type may be used which provide low friction 
characteristics on their outer surfaces yet have good moisture absorption 
qualities as well. For the outer layer, nylon over acrylic yarns of the 
"Cover Spun" type may be advantageously employed. Still other variations 
of "Cover Spun" types of yarns may be chosen according to the various 
considerations discussed above in connection with the optimum 
characteristics of the fibers previously discussed. 
Although the construction of the leg portion 14 and the cuff portion 12 is 
not pertinent to the invention, it would be advisable to incorporate 
elastomeric yarns in both portions to help keep the sock from sliding down 
since the high friction characteristics of surface 20a may need some 
assistance in performing that function when the sock is in dynamic use. 
In the discussion of the relative frictional characteristics of the various 
fabrics, reference has been made to "relatively high" and "relatively 
low". These terms relate to attributes of fabrics which were obtained from 
tests made on commercially available socks including wool, cotton, silk, 
nylon, acrylic and polypropylene socks. The socks were tested wet under 
biaxial stretching with 12% stretch from heel-to-toe and 50% stretch 
side-to-side in order to simulate the actual use conditions. They were 
tested on a constant rate of elongation tensile tester in different modes, 
one of which involved mechanized rubbing the "technical face" (front) of a 
fabric with controlled pressure against the technical face of another 
piece of the same fabric. To simulate the rubbing of a fabric against 
human skin, the technical face of a fabric was rubber under controlled 
pressure against a rubber surface. To measure other friction 
characteristics, the technical back was rubbed against the technical back 
of the same fabric, and also against a rubber surface. Experimental 
friction forces were determined under these test conditions and normalized 
by the area of the test surface to produce results ranging from 1.58 
g/sq.cm. to 21.1 g/sq.cm. "Relatively high" frictional characteristics in 
this discussion and in the claims means friction coefficients above about 
19 g/cm.sup.2 (normalized) as measured in the testing set-up earlier 
explained. "Relatively low" frictional characteristics is intended to mean 
those below about 2.5 g/cm.sup.2 (normalized). 
As mentioned in the example previously given, the surfaces of the plies in 
contact with one another, if both are made of polypropylene texturized 
yarns, exhibited the relatively lowest frictional characteristic, i.e., 
1.58 g/sq. cm. Cottom, acrylic, wool, silk, and nylon fabrics exhibited 
friction characteristics ranging from 4.28 g/cm.sup.2 to 2.65 g/cm.sup.2. 
Of course, there are other alternative materials and construction which 
could effect the same low friction-low friction interface between the 
inner and outer plies. 
As to high frictional characteristics relative to the skin, tests have been 
performed in which various surfaces of fabrics have been rubbed against 
rubber. The technical faces of acrylic wool, and polypropylene knitted 
fabrics have been found by these tests to possess such relatively high 
friction characteristics. Similar tests against rubber with respect to the 
technical backs of certain fabrics were done that revealed that acrylics, 
texturized polypropylene and wool all exhibited similar high frictional 
characteristics. Silk is equally good except that it is impractical 
because of price and because of its lesser durability. 
In certain instances, to achieve the desired low-friction interface between 
the two plies, it is possible to use an inner ply made of a plain or 
jersey knit texturized polypropylene fabric. Its inner surface for 
positioning next to the skin would be the "technical back" of that fabric 
whereas its outer surface would be the "technical face" thereof. The outer 
ply could be made primarily of a texturized polypropylene fabric whose 
inner surface is its technical face and whose outer surface is its 
technical back. The face-to-face arrangement of the two plies produces a 
very low frictional characteristic. If desired, terry loops can be placed 
at strategic parts of the sole and sides of the foot area. Such a 
construction is described in the copending application Ser. No. 234,171, 
of Hursh, Johnston et al, filed Feb. 13, 1981, entitled "Two-Ply Athletic 
Sock". 
MANUFACTURE OF THE SOCK 
The sock may be knit upon a circular knitting machine, single cylinder 
type, such as the "Concept", Model T.S. marketed by Crawford, or the 
Speizman "Carolina", Model Amy, or the Catawba Valley Machinery Company, 
Model CVCS fitted with appropriate "stripping" accessories or 
capabilities. These capabilities allow different yarns to be placed in the 
exact predetermined positions within the sock so that their qualities may 
be used optimally. 
As shown in FIG. 3, the sock may initially be knit in the form of a double 
sock toe-to-toe starting with upper foot portion 16 and continuing to the 
leg (and cuff portions, if any) and finally to the lower foot portion 17. 
Heel and toe portions 19 and 21 may be knitted for reinforcement in 
conventional style. As stated above, the size of the upper sock portion 
should be slightly larger to facilitate the insertion of the lower one 
into it for final assembly. For better fit and hence less likelihood of 
slipping or bunching, the leg-foot relation of each such part should be 
formed as close to 90.degree. as possible, as this conforms to the natural 
stance of the foot relative to the leg when exercising. 
The sock would come off the knitting machine in one layer and would have 
openings 16a and 17a in the opposite regions. Closure or attachment of the 
toe sections to one another should preferably be done in a seamless way, 
i.e., so that there is no appreciable additional thickness or hard spot in 
this region that would be a source of irritation to the foot. To achieve 
this kind of closure, the textile fabrication technique known as "linking" 
may be employed for joining the toe sections together and closing them, 
using the same yarns as are incorporated in those areas of the socks. 
Linking machines of any make could be used, so long as the "linker gauge" 
is compatible with the gauge of the sock. Either a double-chain over 
stitch or a single chain stitch could be used. The latter may be advisable 
as it is simpler and occupies less space.