its not hard per say like a bed liner for a truck, its a coating more like, a facial mask women use? you cannot sand it, but it will resist light scratches. people use it to seal foam because foam is basically a compacted material similar to a kitchen sponge at a micro scale, that's why you hear of it 'soaking in' paints and glues. plastidip serves as a barrier because if something wont stick to foam, itll stick to the plastidip, and the plastidip will stick to the foam. this is similar to chroming pipes. chrome wont stick to steel so they coat it with copper/nickel first.
when you peel it off your car or whathaveyou, it is semi stretchy. heavy coats if the stuff feels like the white plastic bags that or commonly used for soil/mulch/fertilizer in the garden section of home depot, if that makes sense. the texture is like rubber coated plastic like MR lightsaber grips, alternatively, plastidip is also the rubber coating on most pliers in your toolbox (that's what it was made for in the first place).