The inside is made of aluminum fabric for heat and cold retention. This was a gift, and I only tried putting something in it, but I ended up not using it and just storing it. I looked it up and found something similar on the Skater official website, so I'll include the URL for your reference: https://www.skater-onlineshop.com/view/item/000000009579 I did a casual inspection and didn't find any stains, but please understand that this item has been stored at home, so please consider purchasing if you are okay with that.