The best material is probably wire frames. Here's why.
STRETCHING
To stretch the pelt you can use either commercial wire stretchers which are especially made for the job, or you can use a homemade stretching board. Wire stretchers consist of fairly stout wire that has been bent in the shape of the desired pelt. (ill.6) They come in different sizes, depending on the type pelt to be stretched. Wood stretching boards can also be purchased, but most trappers make them. They are usually made out of a soft wood, like basswood or pine. When making a board, cut a one inch board into the same shape as the pelt. Be sure to smooth all the rough edges.
The metal stretching frames, left, will usually fit most hides, while, right, it takes many different sized boards to fit different sized hides.
An advantage of the wire stretchers over the wooden boards is that they are adjustable. The wire can be reduced in size by just squeezing in on the sides to fit into a smaller pelt. Though they are cheaper, the trapper needs a wooden stretcher to fit every possible size pelt.