The friction caused by the piston action of the residual limb is more likely to be between the nylon sheath and the prosthetic sock rather than the prosthetic sock and the amputee's residual limb. Rinse in lukewarm water. Do not twist to remove water. Stretch the sheath length-wise so that it regains its former shape. Hang to air-dry.
Fresh socks give the ultimate in walking comfort.
Allow the cleaned socks to be stored for several days before using. Such a rest period allows the wool fibres to regain their natural resiliency. 5 ply is the thickest and single ply the thinest. You have to learn how many ply socks you need to wear. This may vary from morning to evening, winter to summer, therefore always carry spares with you.