Introduced in the 1980s, honeycombs are built on a simple concept: Trapped air is an insulator that can conserve your hard-earned heat. Since then, makers have scrambled to make honeycombs work even better. Consider these two blackout versions. The budget one has double cells and side tracks to nip drafts, while the high-end one has an extra air pocket to hold in heat. Because there's no universal energy-efficiency test for shades—at least not yet—they can't be ranked, but both high performers qualify for a 2011 federal energy tax credit when installed inside a double-glazed window. Lowering either will raise your comfort level, so look for differences in style, function, and price.