Such “grass stockings” were used by both men and women and especially with fish-skin boots, which, though waterproof, provided little insulation.
Grass insoles used in combination with loose grass absorbed perspiration and water that seeped into the boots. Grass is absorbent and wicks moisture away from the skin to keep it warm and dry.
The absorbent and wicking properties of dried grass are explained by two phenomena. First, as the grass dries, air spaces are created within it. Water is able to move into these spaces through capillary action; just as a paper towel can absorb spilt grape juice, so dried grass absorbs water until it can hold no more. Second, the more grass surface area is present, as when grass is loosely packed inside a boot, the greater amount of absorption. Because grass socks are tightly twined, the exposed surface area is relatively low, absorbs little and in effect “wicks” water to the more absorbent loosely packed grass around the socks. Yuungnaqpiallerput: the Way We Genuinely Live pg. 231