PH wrote:The biggest improvement to how warm I sleep has been the mat rather than the bag - I'd read and understood this a dozen times before changing what was already considered a decent mat (Thermorest) for an excellent one (Exped) and the difference was far more noticeable than I'd expected.
There's mats and there's mats, and Thermarest and Exped both make a big range so which is most insulating depends on which mat rather than who made it. The R Value is the degree of insulation provided, the bigger the value the more insulating. There's slightly more to it than a lab measurement, so if you habitually sleep on your side your hip will provide a pressure point which may ground out when on a thin mat and give you a point of heat loss, though IME it's more to the point that on hard ground I get a sore hip, so prefer thicker over notionally warmer to some degree.
Mats are more significant with down bags because the insulation is actually still air trapped by the notional insulator, and when compressed by body weight the air around down is squeezed away far more than the air inside hollow synthetic fibre, so while down is generally a better insulator than synthetic fills that's not the case underneath you. So why do bags have down underneath? Because people don't sleep in a completely static manner and what constitutes the "side" of a bag changes regularly through a night, and/or they might like to sit up in a ba and keep warm. There have been experiments with "top bags", with no insulation underneath but a slot for a mat, and as long as you lie perfectly still on your back and don't create space for convection currents they'll work okay. For those of us that move about a bit more the theory is not up to the practice. And stuff like sitting up in your pit while cooking breakfast just doesn't work so well!
For light weight I very much like the Neo-Air mats. Very low bulk too, and available in an X-Therm model with a good R value. Not cheap though, and more of a faff in a chair kit than a self-inflater (I find sitting on the ground with no back support quite uncomfortable for more than a few minutes so this matters to me, I'm sure it's irrelevant to many):-(
Pete.
Often seen riding a bike around Dundee...