Cotton is the only fiber that can be bleached. No matter which fiber you choose, you must still rely on ply for daily changes in residual limb size due to edema or atrophy. In specifying prosthetic socks for veterans, VA requires manufacturers to use wool yarns of a particular size. The thickness of a sock can be measured by a thickness guage. Measurements of wool socks knitted using the specified yarn size define each ply within a narrow range.
Prosthetists allow for that thickness when making limbs.
Socks of 100 percent cotton and 100 percent acrylic will have a consistent ply fit, but not necessarily the same as a wool ply fit, because no other fiber has the fulling properties of wool. Relating ply to the fit of the prosthesis is more of a challenge when socks gain thickness from Lycra spandex. This is because as the Lycra, which draws the yarns together, is stretched, it pulls the yarns apart and the sock becomes thinner. Such stretch helps the sock contour to the limb and fit more smoothly. The difficulty lies in determining the stretched thickness of the sock on the limb so that the prosthesis will fit properly.