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Huh? Water has a significantly-higher specific heat capacity than these dry powders, so will definitely stay warm many, many hours longer. I can say this with e

by SamBam 5y ago

Huh? Water has a significantly-higher specific heat capacity than these dry powders, so will definitely stay warm many, many hours longer. I can say this with experience: the hot water bottle I put in my bed at midnight last night was still warm at 7:30am, while the buckwheat cushions I got my kids stay warm 15 minutes tops, no matter how hot I make them in the microwave. Even with the very best dry microwavable pillows, there will be at least a 20x difference in heat capacity. And your premise doesn't make sense. A hot water bottle under the blankets will also be at body temperature after (many) hours. There's no reason for it to get colder than the wheat pillows. And the fabric covering feels just as warm.

masklinn 5y ago
IME they're not necessarily wrong, HWBs without fabric covering (which used to be relatively frequent a few decades back for some reason) would feel really rather cold in the morning, the rubber feels clammy. And because they'd be way too warm early on, you'd push them to one side and get close but not too close. So body heat wouldn't really keep them warm once their eat is expended. With a woolen cover or padded cotton, the heat release is much slower and more uniform, so the HWB is more comfortable, last a lot longer, and because you only touch (relatively insulating / insulated) fabric it never feels really cold.
- hilbert42 5y ago
  Yeah, I recall as a kid it was easy to scald or burn oneself on an exposed rubber bottle, and of course it cooled much more rapidly (I too remember that cold clammy feeling in the morning). However, the more usual situation was to put the HWB in a knitted woollen jacket. That kept the heat in and it didn't burn one and was still warm in the morning.
zokier 5y ago
I think the effect is more related to that water conducts heat well, while cereal pillow will function as insulator.
- masklinn 5y ago
  It's mostly a function of the rubber, while it's not a great conductor it's also not a great insulator. So the water will release heat relatively rapidly, and once it's cooled down to ambient temp the rubber will pull water from your skin if you touch it (it also tends to feel somewhat clammy in my experience). That's why wrapping the rubber container in a woolen or padded cotton cover mitigates the effect a lot, it will slow down the heat release, and once the water has cooled down it'll limit the heat transfer back into the container, and thus won't feel cold.

by SamBam 5y ago

masklinn 5y ago

IME they're not necessarily wrong, HWBs without fabric covering (which used to be relatively frequent a few decades back for some reason) would feel really rather cold in the morning, the rubber feels clammy. And because they'd be way too warm early on, you'd push them to one side and get close but not too close. So body heat wouldn't really keep them warm once their eat is expended. With a woolen cover or padded cotton, the heat release is much slower and more uniform, so the HWB is more comfortable, last a lot longer, and because you only touch (relatively insulating / insulated) fabric it never feels really cold.

hilbert42 5y ago
Yeah, I recall as a kid it was easy to scald or burn oneself on an exposed rubber bottle, and of course it cooled much more rapidly (I too remember that cold clammy feeling in the morning). However, the more usual situation was to put the HWB in a knitted woollen jacket. That kept the heat in and it didn't burn one and was still warm in the morning.

zokier 5y ago

I think the effect is more related to that water conducts heat well, while cereal pillow will function as insulator.

masklinn 5y ago
It's mostly a function of the rubber, while it's not a great conductor it's also not a great insulator. So the water will release heat relatively rapidly, and once it's cooled down to ambient temp the rubber will pull water from your skin if you touch it (it also tends to feel somewhat clammy in my experience). That's why wrapping the rubber container in a woolen or padded cotton cover mitigates the effect a lot, it will slow down the heat release, and once the water has cooled down it'll limit the heat transfer back into the container, and thus won't feel cold.