ABSTRACT
The present work discusses the friction between foot, socks and insoles in order to provide comfort and avoid the blister development caused by shear. To reduce the risk of developing blisters and ulcers, it is recommended to set low friction on the interface of socks and insoles to allow foot sliding, and high friction on foot skin and the inner surface of sock to provide appropriate level of resistance to avoid excessive movement. The best friction arrangements to achieve the above assumption are to use cotton socks as well as insoles of low friction coefficient when they rub cotton surface.
 
The friction coefficient generated from bare foot and foot wearing socks of different cotton content when sliding against insoles is investigated. Socks of different cotton content as well as 13 types of common insoles were tested to determine friction coefficient between socks and foot skin as well as socks and insoles.
 
It was found that friction coefficient increased with increasing cotton content of the socks, where friction coefficient displayed maximum values for socks of 93 % cotton content, while polyamide socks showed the lowest friction coefficient. Based on the experimental observations, it can be recommended to set low friction on the interface of socks and insoles to allow foot sliding inside footwear, and high friction on foot skin and the inner surface of the socks to provide appropriate level of resistance to avoid excessive movement. The best friction arrangements to achieve the above assumption are to use cotton socks as well as insoles of low friction coefficient when they rub cotton surface. In addition to that, use of insoles of low friction coefficient can reduce the shear force on foot sole to avoid skin abrasion, friction blisters and ulcers for people who used to wear shoes without socks. The significant variation of the values of friction coefficient of different types of insoles should be considered and the friction properties of the insole materials should be developed to fit people of heavy weights.