Here's what other sites are saying:
Introducing an important innovation in windscreen design, the Vari-Vent from Trail Designs! Traditional/Classic/MSR-style windscreens require air to come over the top of your screen and by your pot to fuel your stove. Windscreens with perforation along the bottom don't block the wind and require you to do unnatural acts with boulders. The patent pending Vari-Vent technology provides a series of variable vents along the bottom edge of your windscreen, allowing you to close off the upwind side while keeping the downwind side open. Further, by allowing you to customize your windscreen venting in the field, to fit your system, you can get it closer to, and higher up, your pot. The edges are rolled to make it stronger and safer to use. The screen will fold flat for storage or you can wrap it around your fuel bottle.