Many people use mylar, and most find out quickly it is a pain in the ass to keep clean. Some people swear by flat white paint. Is there an in between, something like this maybe?
Find a Rust-Oleum Specialty 10 Oz. Flat Reflective Spray Paint (6-Pack) - 182794 at The Home Depot
Find a Rust-Oleum Specialty 10 Oz. Flat Reflective Spray Paint (6-Pack) - 182794 at The Home Depot