I love using HWBs (Hot Water Bottles) while winter hanging. Absolutely brilliant!!
Been using them for about five years now without an incident. So far I have tried cozies made of single and double layers of reflectix. The single layers let out a lot of heat right away thus are useful for prewarming bedding. They give me about 4-5 hours of useful heat. The double layer cozies are deceptive because at first it seems as though they aren't letting much heat out. Give them time! Takes about a half hour before they get rolling. They give me 7-8 hours of useful heat. Meant to try a triple layer cozy, just to see how that performed, but am so happy with the double layer that I haven't yet.
I've done dozens of full rolling boils in doubled reflectix cozies using the same quart Nalgene containers without an issue. With "imitation" Nalgenes I've had them deform and delaminate from pouring too hot (full rolling boil) water in 'em while in a double layer of reflectix cozy. Pour hot water in them again with the lid off and they mostly return to shape but they have never relaminated. Still using them (still work, still haven't leaked) yet the writing is on the wall. If using a nonNalgene bottle, I go to a small boil (tiny bubbles sticking to sides of pot) and a single layer of reflectix cozy. Less heat for less time, but also less risk.
Happy Trails!!
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