Vacuformed canopy

Age of the material. It has degraded over time. Possibly the materials they used are partly to blame. I remember reading somewhere that this stuff turned yellow after being on the model if it wasn't protected. Is your machine getting the plastic too HOT? Are you exposing it to the heat too long?

Try less heat for shorter period.

I have two sheets of the material left. I will try your suggestion about the heating.

I have tried all sort of heat ranges with my last two sheets & still the same problem. But I did try a piece of clear material from one of those presentation binders one can find at an office store. The material will not fog or discolor and seems to take any amount of heat I give it. It snugged down nice over my wood master but showed some minor scratches that were on the master. I skimcoated the scratches on the master with a very thin plyable coating of fine milliputty. I resanded the wood master with 2400, 3200 & 4000 grit sanding pads so it looked polished which solved the problem.

K&S Butyrate,..sheets come in different thickness, (I use .015 for canopies), and when vacuformed, it stays very clear. Dave.