I make to covers for my dog beds in the envelope style. I make fleece for the winter time and 100% cotton material for the warmer months. I use foam for the inside of the bed. I found some at a discount store at a good price. I double it so it's nice and thick for them. One thing you should NEVER use is cedar chips in a dog bed. It is a very common allergy to dogs. I bought a dog bed at a store and my dog chewed it and ripped it apart. I didn't think anything of it until I saw the cedar chips in it. He was trying to get the cedar chips out I think. He has never ripped any of the foam beds up at all. Good Luck and I can't wait to see what you make.