Shaped saddle pads are sometimes padded with felt inside of quilted cotton.
A shaped (or "numnah") saddle pad is saddle shaped, and is designed to be used alone, or with a square saddle pad. A shaped / numnah pad should only be slightly visible below the saddle.
Wool felt is made out of compressed wool. Felt is graded into 15 categories, and the lower the grade, the higher the felt is in virgin wool, strength and compression ability. Saddle pads are made from F10 - F15 wool felt, and pads that are F10 or F11 will be of superior quality. The benefits of wool felt are that they are good at absorbing shock and preventing pressure points from ill-fitting saddles. Wool felt is also effective at preventing heat buildup, and for wicking away sweat.