Step 3: 3. Tin Foil Layer
I have seen some tutorials do this, and some not, it is really up to you. it is an added layer of protection from the resin seeping though to your carpet, and I highly suggest it. Use squares of the foil, taping and overlapping them as you go. You should now be ready to start the glassing.
Protecting the interior is very important as this stuff will not come off. I suggest placing newspaper, or drop plastic all around your work area. Also, if you like you can also put a sheet of plastic between your trunk and cabin to prevent fumes from getting in and stinking up the car for a few days.