Sorbothane is a top of the line shock absorbing material without being squishy. It does add some weight to the shoe. The sorbo air adds a few ounces which is noticeably in all shoes but particularly light weight shoes (like running shoes). I use the sorbo "air" in both running and some of my walking shoes. Sorbothane helps to reduce sore legs and should help those with bad knees. Sorbothane "ultra", which Holabird also sells, is about as good as it gets for both cushioning and pronation control but adds much more weight and is thick (ie, need more room inside the shoe). I don't use the "ultra" in running shoes but use it in walking or gym shoes. If weight or thickness are not a problem, buy the sorbo ultra. If weight or thickness are a problem, buy the sorbo air.