Likely a heating pad under a towel I would guess

I have a couple of these from K&H brand. A heating pad lies underneath the blanket. You need to be able to plug it in. I run an extension cord through a tiny window opening. It is 4V and only turns on with the cat’s weight so much safer than a normal heating pad or blanket. Mine are going on 4 years of use. Easy to clean and foldable. 1/2 🧵

Our Decker came to us 14 years ago and had a heated house out of plastic tote. Had pressure sensor heating pad and was raised up on foam. Would heat two bricks on the grill every day and slip them under the house. Toasty!

They boil it before serving