These "Thermals" are good for the price but if your thinking that these and a pair of PJ's in the desert in  winter or even the mtns. or cold weather area's will keep them warm think again. I'm a US Marine and know from experience that cold climate is the hardest to survive in. "Layering " is the answer. As the Temp drops ad a little layer of clothes starting with these and something to stop the chill going down your neck. Then build more until bed time then in the mourning do the reverse. Also don't skimp on a good sleeping bag. Most company's that advertise 20,10,0,etc... are not being forthcoming. Suggestion: Get a nice -20 and a cheaper +20. Then put the smaller of the 2 usually the -20(Huh) inside the +20. The worst that can happen is they'll be too warm. I'd recommend these thermals but wouls suggest athe more expensive brands.