Sims, Kick-eez, Pachmayr (decelerator), and a myriad of others. The 'soft' rubber pads all pretty much use the same material, a stuff called sorbothane. It's a ruber like plastic that starts soft but reacts to energy by firming up.. The Sims products us a different internal structure the is supposed to increase their effectiveness. The Pachmayr pads have a steel plate added between the backer plate and the rubber portion to help with breakage of the plastic backer.. It helps if you are trying to curve the pad slightly to fit a buttstock.. I have seen Kick-eez pads that collapsed and hardened...I have no idea why. I have not witnessed that with the Pachmayrs and I don't have enough experience with the Sims...yet. I prefer no surprises and so usually pick the Pachmayrs as they are quite concsistant although I have noticed more flashings and overflows of late. If you are extremely recoil sensitive Pachmayr makes a 'Triple Magnum' pad. It consists of three seperate types of material the center section I a firm foam rubber..the base a hard plastic(for the mounting screws) and the face a soft rubber material. It comes with a metal 'peg' which is inserted into a hole in the pad to hold the weight of the weapon off the pad, which is 1.5 inches thick and most assuredly will deform under constant pressure as in standing in a rack. The peg is a bit of a hassel but the pads erally soaks up the recoil without the tendancy to pinch when used on the hard kickers. Try the Pachmayr decelerator pad in whatever style suits you and you will be happy... ----NOTE--- All the soft rubber pads need proper installation to finish well..
