Scientists at MIT have discovered a see-through film that rejects 70 percent of the sun’s incoming heat. The material is thermochromic, meaning that it changes color in response to heat, getting darker at higher temperatures. Sticking it on windows could potentially make air-conditioners, which are greedy energy consumers, become obsolete. With the cost of cooling down America’s homes standing at around $29 billion annually, this window coating offers a simple yet effective solution.