[caww]

My dad had hunting beagles....they had a huge fenced in area to run which was up against a barn....plus a dog opening into the barn which was divided off and filled with straw which was changed as needed. They would snuggle right into the mound when temps dropped low. They never felt the least cold when we went out to feed them. For some reason it was understood straw was better than hay to keep animals warm.

[CommerceComet]

The doghouse that this dog used had insulated walls and roof and 12-15" of straw on the insulated floor. When I changed straw, the dog got so excited that it was hard to keep her out so I could finish the job. On cold nights, you could move aside the canvas door flap and put your hand inside and it felt like room temperature after she had been in there.

I don't know about differing insulating qualities. I used straw because it was much cheaper than hay.