One of my favorite outdoors stores was doing 10% off of one item for one food item for the food shelf, so I picked up a Thermalite (among other things).

First observation- the ditch kit was reorganized so I can have that, rather than the Heatsheet bivy. Much better for cold weather.

Second observation- it fits in any pouch that fits a Nalgene quart, or 4-5 M16 magazines. Or a Nalgene cup.

That it fits in the Nalgene cup means you can protect it in storage, and the pouches mean you can have one with you easily enough.