Far as I recall, it's a fiberglass cover. same stuff welding blankets are made from.The place i bought the grill from threw in the winter cover for no extra cost but a welding blanket would do the trick also. Im not sure what campchef uses as an insulation in their blankets but mine weighs a ton.
Corey
The welding blankets are pretty heavy too.
Yeah, it's a little dirty, so I may spring for a new one this fall. It's seen a lot of cooks. To open the grill, I just grab the edges near the top of the lid and fold it up on top.