I filled one with some spray-in type insulation from Lowe's. It comes in a square, plastic covered, blue & white bail and it is allergy free, itch free, etc. It says R-19 R-25 R R-30 on the side. The stuff packs good too and makes the bag nice and firm. I also added some lose sand to the mix to give it some weight (not much though). I also filled one with old rags and clothes, it was okay but, the other was better.