The coat of the yak is composed of three different types of fiber that vary greatly in appearance and characteristics. The quantity of fiber produced by one yak is dependent on factors such as sex, age, and breed of the yak, and the proportions of the different layers vary throughout the different seasons.
- The coarse: Mostly used by nomads in tent making, this fiber has a size range of 79-90 microns forming the outer coat of long hair that characterizes the appearance of the yak.
- The mid-type: With a diameter size between 20-50 microns, this fiber is naturally strong but not stronger than the outer layers to make ropes and tents and not as fine as the down fiber for the textile industry.
- The down fiber: This is the finest fiber (16-20 microns) and is generally shed by the animal during late spring/early summer period. Therefore, this fine layer needs to be harvested before it is shed in the summer season. Down fiber, and fewer sweat glands, are two examples of how yaks have adapted to survive extreme cold temperatures (sometimes as low as -50 °C, or -58 °F) and altitudes well above 3000m.
Yak wool has similar properties to other animal fibers, including breathability and static-resistance, but has been proven to outperform sheep wool in a number of areas:
- Warmth: In woolen garments, air pockets are created between the fibers that reduce the rate of heat transfer, and lanolin (a hydrophobic grease present in wool fibers) allows the wool to keep you warm when wet. Yak wool is rich in myristic acid, a type of hydrophobic fatty acid. Independently conducted tests on yak down suggest that it is between 10-40% warmer than Merino wool.
- Softness: Cashmere is known in the textile industry as one of the softest wools with a fiber diameter of less than 18.5. The diameter of the down fiber of the Yak also ranges 16-20 microns making its softness comparable to that of cashmere. Species-specific DNA probes have been developed to identify yak, which is used to quantitatively test yak-cashmere blends. Although cashmere has already been firmly established in the market, yak wool has potential to be sold as a luxury product due to its softness and the (currently) sustainable and eco-friendly means used for gathering the fibers.
- Breathability: In general, wool’s comfort comes from its thermo-balance characteristics. The breathability factor of a material depends on its ability to absorb moisture relative to its weight and then release it into the air. The higher the value the better the textile is at adapting to humidity level changes. Wool can absorb over 30% of it's weight in moisture, greater than cotton (25%), and far greater than polyester (1%).