I copied this from the National Hosiery Association website:
Sock Blends
Most socks are blends of two or more yarns or fibers in order to receive the benefits of each. These fiber are either natural or manufactured, but natural fabrics frequently will not give or stretch. Following are some sock yarns and their benefits.
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natural fibers
COTTON
Cotton is soft and heat-resistant. It absorbs moisture from the foot, is breathable and provides shock absorbency.
LINEN
Linen is strong, durable and yet lightweight and able to absorb moisture. It is often used to add strength to socks.
RAYON
Rayon is a fiber made from various solutions of modified cellulose. It has a soft hand, high moisture absorbency and retention, and good dyeability and washability.
SILK
Silk fibers are obtained from the cocoons of various types of silkworms. They are soft, lightweight and add luster, but can be expensive.
WOOL
Wool is the soft, curly hair of sheep that is spun in to yarn. The wool family includes Shetland (Scottish) and Merino (Spanish) wool, which are soft and of high quality. Most woolen yarn used in socks is made from standard grades produced in the United States, Australia and elsewhere. Wool is warm, sturdy and durable. It has a crisp, resilient hand and excellent insulating properties.
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Rebeckah: There are also other *hair fibers* like: cashmere, angora and mohair.
This is copied directly from Sock-Dreams.com website{Orkney Angora page}:
Angora wool is the lightest natural fibre known. The hollow structure of some of its fibres makes it ideal for thermal clothing. ANGORA fibre can only be produced by angora rabbits. (Angora goats produce mohair.) The angora wool fibres measure 10-13 microns whilst the highest quality lambswool is 18 micron - very fine and an excellent fibre to blend with the angora. It is comfortable to wear next to the skin, allows the skin to breathe but absorbs moisture and helps to maintain a steady temperature at the skin surface, in other words it keeps you WARM & COMFORTABLE.
Warming & Therapeutic Effect: Angora wool improves blood circulation, giving natural benefit to the wearer. Research in Germany has demonstrated that angora wool is up to 3 times warmer than sheep's wool. This warmth-giving therapeutic effect is particularly beneficial for people with cold painful joints, sciatica, arthritis, muscle tension, kidney ailments, rheumatics, chilblains, circulatory disorders etc.
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Cashmere from wikipedia.org {edited}: The Cashmere (Kashmir) or down goat produces a double fleece consisting of the fine, soft undercoat or underdown of hair commingled with a straighter and much coarser outer coating of hair called guard hair. In order for the fine underwool to be classified and used as cashmere it must be de-haired. De-hairing is a mechanical process that separates the coarse hairs from the fine hair and after de-hairing the resulting "cashmere" is ready to be dyed to color and converted into yarn, fabrics and garments. Natural colours of grey, brown and white.
Cashmere is characterized as luxuriously soft, with high napability and loft. It is noted as providing a natural light-weight insulation without bulk. Cashmere is extremely warm (in order to serve its original purpose of protecting goats from cold mountain temperatures.) Fibers are highly adaptable and are easily constructed into fine or thick yarns, and light to heavy-weight fabrics. Appropriate for all climates, a high moisture content allows insulation properties to change with the relative humidity in the air.
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manufactured fibers
ACRYLIC
Acrylic fibers are man-made and are generally warm and lightweight. They are used in casual, dress and athletic socks. Acrylic keeps its shape well. Its other properties include resilience, softness, easy care, minimal shrinkage, rich coloration and the ability to wick sweat away from the foot.
NYLON (POLYAMIDE)
Nylon is the first and oldest of the true synthetics. This fiber is famous for its strength, abrasion resistance, dimensional stability, soft hand, elasticity and easy-washing and quick-drying characteristics. It is used in men’s dress socks, in novelties and as reinforcement with other fibers. It is a durable, shrink-resistant fiber often used in blends to add stretch and strength to socks.
POLYESTER
Polyester is a man-made fiber that is abrasion-resistant, has excellent washability, and is fast drying. It is readily heat-settable and dyeable. Polyester is used in men’s and boys’ dress socks, in decorative applications such as cross dyeing and jacquards, and as reinforcement.
POLYPROPYLENE
Polypropylene is a member of the polyolefin group of synthetics. Inexpensive and lightweight, it is strong and soft, but dye resistant. It adds strength, durability and stretch to socks. Like acrylic, nylon and polyester, polypropylene can be used to enhance the thermal and wicking properties of socks.
SPANDEX (ELASTANE)
Spandex is a generic term denoting a man-made elastomeric fiber used in place of rubber. It can stretch to more than five times its relaxed strength and fully recover. Spandex is used in support and light support products to shape and compress the leg. Spandex yarns are often covered with other yarns and are widely used in sock tops for “stay up” holding power. It provides better size ranges, improved fit and added comfort.
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comfort features
ANTIBACTERIAL FINISHES
This durable finish is added to socks to control the growth of odorcausing bacteria. It usually will not wash out for the life of the sock.
BRUSHED
Brushes can be used to produce a very soft and fluffy napped surface in socks.
COMFORT OR ROLLED TOPS
Knit-down or welt tops can be turned over and knitted down for non-binding comfort. These are less likely to ravel and come apart.
SUPPORT
Support socks are made of nylon or polyester with spandex or other elastic fiber added to give support to the leg and reduce leg fatigue. Support provides graduated compression to the leg. Support no longer means a heavy surgical item - today it means fashion and color as well as durability.
TERRY OR CUSHIONED
Terry is used as a “liner” in socks to increase cushioning. It can be used in the foot of the sock or as a liner in the whole sock.
THERMAL
Thermal socks are winter-weight socks favored by skiers, skaters or others that spend a great deal of time outdoors in cold weather. They can be made of heavy acrylic, wool, polypropylene or a blend of fibers.
WICKING
Wicking is the capacity of a fiber or yarn to transport moisture away from the foot for evaporation.