Well Balanced Cat

I caught Frisky sleeping on top of the compost heap. It's mainly old sticks and twigs from trimming and chopping down trees as the grass cuttings go in the council green bin. I do understand that it probably retains a lot of warmth, what I don't understand is how it hasn't collapsed (see extra) as there is a large void underneath all the sticks he is laying on. He obliged by looking up long enough for a blip and then went back to sleep. Sun and warmth makes him so sleepy.