When printing etchings and engravings, the function of the felt is to press the paper into the grooves of the plate. The grooves are filled with ink. When the paper is pressed into the grooves, the paper absorbs the ink.
Do not use more felt than necessary!
With a normal etching, 2 mm or 3 mm thick felt is sufficient to perform the above function. With deeply bitten plates or blind pressing it is necessary to use thicker felt (or several layers). If you use more felt than necessary with a normal etching, then you will have to put more pressure on the press to get the same result. After all, the "contact line" becomes wider with thicker felt.
Felt is made of wool. With woven felt, there is a woven structure in the felt that keeps the felt together. The felt is therefore softer and stronger. Woven felt is used in paper machines, for example, to give structure to the paper surface. Woven felt can sometimes be an advantage for printing etchings with many fine details. However, if the woven structure is too clear, this structure will also be printed, which is not the intention. The internal structure should not be visible from the outside.