Place one hand in the center of the saddle and lightly press down. This helps to secure the saddle in place as you test for panel pressure. Run your other hand between the front of the panels and your horse's musculature and feel for any uneven pressure under the points. The front panel should not pinch the withers in any area.
While maintaining pressure on the top of the saddle, run your hand, palm up, under the entire panel along the back feeling for even pressure. You may also raise the sweat flap to ensure that the panels fit snugly and evenly on both sides of the withers and along the back to check for bridging.
Bridging is a space near the center of the saddle seat where the panels do not make good contact with the horse's back. Wool stuffed panels are almost universally considered superior to foam for the following reasons: assuming correctly designed panels, wool conforms to the many shapes of the horses back and can be adjusted if necessary to correct for a multitude of fitting problems. You cannot, however, correct for a poorly designed or incorrectly fitted tree.