Actually that thing is foamed polyurethane thermal sitpad best used when one has to sit in cold rocks or wet ground for hours. It's extensively used by the military and hunters.
Great shot. They should have hobbled the front legs and one rear leg. And used thicker rope. That stuff will cut the horse to ribbons.
Done properly the horse wouldn't be harmed, people wouldn't be harmed, one person could put the shoe on and the horse would then be hobble broke. Meaning if he ever got caught up in barbed wire, he wouldn't thrash and kill himself.