I love mylar....I use the 2 mil x 50ft for $30 (bought off ebay) I have 48ft to cover (4 - 12ft long walls)

I have been using the same mylar for about 4 years now...couple hints..use duct tape where you are going to mount the mylar to prevent tearing....dont let it get wet or have condensation on the mylar.... that dulls the reflectivity