USOutdoor.com:

MSR Heat Exchanger An engineered cooking accessory for improving fuel economy while melting snow or boiling water on longer trips. Not recommended for delicate cooking or simmering, since any spillage will be difficult to clean out of the unit.Features:The MSR Heat Exchanger increases efficiency up to 25% by capturing heat normally lost to the atmosphere. The Heat Exchanger saves time, fuel and weight. Rolls up for convenient storage inside your small pan. Unique waffled design channels the heat from the stove up the sides of the pot to increase efficiency. Compatible with all MSR 1.5- and 2-liter pots. Weight: 160.0 grams A metal collar attaches securely to MSR 1.5 or 2.0L smooth-sided pots, or any similar pot of the same dimensions. Corrugated surface channels additional stove heat into the pot through the sides. The unit can improve heat transfer, and fuel consumption, by up to 25%.

Moosejaw.com:

Free Shipping. MSR Heat Exchanger (Spring 2009) The Heat Exchanger by MSR increases the efficiency of your stoves up to 25%. The unique waffled design channels the heat from the stove up the sides of the pot to increase the heated surface area of the pot. The Heat Exchanger is compatible with all MSR 1.5- and 2-liter pots. (with the exception of the Titan 1.5-liter)Weight: 6 oz/170 g