Just had to share a trick I leaned from Kyle Voss, the guy from Fab Forums I like.
I do a lot of fab'ing and use a lot of cardboard for templates as well. I use to collect used stuff and cut up boxes too until I saw his video (see below). He uses RAM Board—the stuff for putting on hardwood floors when a house is being built. It's great for fabricating because it is stiff, durable, cheap and thin enough it won't offset your measurement like corrugated board will. You can get it at Home Depot, and I always look for a damaged roll, then go to the sales guy and get him to mark it down to half price or less. I read on the Aircraft Spruce forum that airplane and race car guys say you can saturate the stuff in water and it will conform around larger parts. Rumour says it will dry that way, preserving the contours. This would make sense because the glue used in it probably isn't water soluble as construction guys would be tracking wet, dirty boots across it in a new house. But I've never tried this.
It's great stuff, and if you want thicker you can spray with adhesive like 3M Super 66 and layer it. A trick I learned is that if you spray it with PlastiDip and let it dry, you can roll it in a slip roll and it will keep its shape long enough to cut a curved pattern, which is pretty cool. I also use it in my bead roller to test new patterns out before using the metal sheet.
I pre-cut it off the roll and store it flat so it is ready when I need it. Here's Kyle's video:
