Question

is cardboard a good insulator

Answer 1

It might be but it's highly flammable since it's a paper product.

Answer 2

Well yes, it is considered to be a good insulator because of its structure or in other words , because of its molecular makeup.

"Cardboard is considered a good insulator due to its molecular makeup. The material also has a type of double walls that prevent heat transfer. Cardboard is also considered to be strong against winds."

http://www.ask.com/question/why-is-cardboard-a-good-insulator

Answer 3

Cardboard is paper, and paper has been used as insulator primarily within capacitors as a dielectric, but as has been mentioned "flamable"