Sivaoans made them they were made to repel water, and quite strong. They were made for:

• Bridge crossing, during the Walk the first contact team had to cross a raging river. Halfway across a large object muddy water, in the fast moving along filled with runoff from the thunderstorms that passed that point upstream,
• Traveling tents along with ties either on the ground or in a tree, Also the Walk it was made into a map, which got lost during the crossing of the river.

They were quite versatile.

• Before the Walk some of the material was used along with sugary glue to make a replacement tunic for one of the members. (TOS novel: Uhura's Song)