Here is the problem: The bars of a saddle, which rest on a horse's back, rarely completely conform to the exact shape of the horse's back. I want to make a rubbery or heavy dense foam shim which will fill in the voids between the saddle bars and the horse's back so there is a perfect fit. In my mind's eye, the perfect material would have the consistency of tire rubber, and be about 1/2" to 1" thick. You could cut it so it matches the shape of the saddle bar and glue it to the saddle bar. When you were ready to fit the saddle to a particular horse, you would put the saddle blankets or pads you usually use when you saddle your horse on the horse, then do something to make the rubbery compound slightly viscous. Maybe peel off a paper cover, or spray it with some chemical. Then you'd put the saddle on the horse, and tighten the girth, i.e. saddle him. Perhaps you would even mount the horse and just sit in the saddle for say 30 minutes to an hour while the compound slowly fills in the voids and then sets or hardens. Thereafter that particular saddle would fit that particular horse like a glove, at least until the horse's back changed due to muscling up, fattening up or losing weight, pregnancy, age, etc. But the shims should last for a few years. Then you could just do it all over again. Because there would be a blanket or pad between the saddle and the horse, heat would not be too much of a problem. The compound could end up being hard as a rock, altho ideally there would be a little bit of give in the substance. The substance can't be runny, and it can't harden up super quick. If it takes an hour to take a shape and then you would unsaddle the horse and turn the saddle upside down and let the substance finish curing till it was permanently set, that would work too. I did make a shim out of Bondo, but it was a real mess, and I dread doing that again. Thank you.