Until today, every historic example I had ever seen was cloth.
I never expected to run across two examples of knitted pockets in this fabulous online collection.
As the curators state:
"Few pockets made by knitting or crochet seem to have survived in Britain. Perhaps few were made in the first place because the techniques and materials produce an elastic and relatively open effect less suited to the making of weight-bearing containers than woven cloths or leather. These latter materials also offer the added benefit of a tight, smooth and durable surface that moves well under garments such as petticoats or aprons. However, many embroidered pockets were made and used with textured and delicate surfaces that did not offer this particular benefit. The scarcity of surviving knitted or crocheted pockets contrasts with the popularity of knitting and crochet as domestic crafts during this period and the survival in museums of large numbers of other items made by these techniques, from shawls, stockings, caps and bonnets through to purses and bags, table mats and other household items. It is possible that some pockets made in this way were unravelled at the end of their useful life and the yarn used to make other things. "
Pocket 1 (in a traditional shape) is here. Be sure to click on the enlargement to see the stitch pattern.
Pocket 2 (a double-decker single pocket) is here.
Both are cotton, which makes sense given its relative lack of elasticity compared to wool.