Modifying cardboard to the point where it becomes as useful as other materials like wood.

I wanted to make cutting mats for free so that I could paint, solder, and otherwise destroy them without caring. A real rubber cutting mat from amazon can cost up to $30. There are some small dollar store ones that are honestly pretty good too, but they are very small. I started to simply paint cardboard squares and this worked ok, but i looked into it and found that people use shellac to harden cardboard and make it water resistant. I also saw a video where a teenager as a joke built a house out of cardboard boxes and stayed in it for one night. I also have seen articles about and even commercials for this kind of slow moving injection foam that fills up spaces completely. If you could fill treated, painted waterproof cardboard boxes with some type of foam maybe this could make them like very large densely insulated bricks. Take a metal structure for a carport or even sticks and attach the boxes to that and then put metal roofing on the outside and house paint or maybe even drywall and/or wallpaper on the inside, maybe held together partially by duct(or other) tape, and this on top of a level wooden platform could be a very cheap way to make a small insulated building. This is slightly above homeless level tech, but if it worked it could be amazing, maybe it could be better insulated than a real house. I don't know if this would be cheaper than metal buildings or not, but it just might be, and i'm sure it would be better insulated. So houses are like the max level of cardboard enhancing, I might need to repeat some of this info on the small buildings page if i ever work on it, but when it comes to the cardboard, there's also small things like desk organizers and cutting mats, and small furniture like book shelves or even desks. I like the youtube channel the cardboard genius, especially because he made me aware of using shellac on cardboard, but there's lots of people who do this.