The Primus Windscreen and Heat Reflector for Stoves focuses more warmth on your food and blocks pesky breezes, shortening cooking time and saving fuel. The flexible aluminum sheet fits over most small stove burners, and folds up when not in use. It also works pretty well as a rain collector if you sit it atop your water bottle.
Piece missing twice!
I bought this windscreen for a trip in specific. Unfortunately when my order came, it didn't have the base ring to place around the stove, Backcountry immediately sent me a new replacement (sealed packed) and that set was also incomplete. I would have kept it if it was easy to cut myself in order to rig it to my stove, but the edges are extremely sharp and didn't want to get hurt. If you order it, make sure you get three pieces as shown in the images.
Buy it if it didn't come with yours!
I have a Primus multifuel stove much like the one pictured above and the difference in boil times is night and day when using the heat reflectors. Sure they're just soft bendy aluminum but if you went all Macgyver and made your own out of popcans the thinner metal would disburse the heat more quickly. Seeing as they ARE just soft bendy aluminun you can't really break them like some of the fancier and more expensive ribbed metal rings that serve the same purpose.
Again, if these did not come with your stove, buy them! You will cut down your boil times significantly.