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Comment by ColinWright | Hacker News Reader

Also discussed here:

https://news.ycombinator.com/item?id=30024127

We now use "Wheat Bags" ... cloth bags, usually cylindrical, filled with wheat. Heat in a microwave and use where one would use a hot-water bottle, but without the danger of a leak.

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I use these too, though ours are made with corn for some reason. I guess the friends who gifted them were hanging with the corn crowd on craft-Pinterest or something. They smell like sweet Corn Nuts when heated, which is a pretty pleasant effect.

We do have a cylindrical one but the two biggest are shaped like mini pillows, more rectangular patterned.

Combine them with a lap blanket, hot tea, brand new thick winter socks, insulated slippers, a hoodie, 50 push-ups before work and a 400W zone heater, and you will be able to survive my office in the winter :D

Exactly this haha. Even a relatively mild workout keeps my body warm for hours. For cycling in the winter (which feels especially cold after a warm bed) I used to take cold showers before going outside. I can really recommend this, as the outside temperature feels way more pleasant this way. Instead of shivering the whole trip, I actually enjoyed going outside. Besides, it mentally wakes you up like nothing else.

Edit: and indeed, don't forget the winter socks! I prefer them in wool. Also a baggy fleece sweater/vest made of polar fleece (which I can't find anywhere anymore) with the thickest and highest collar possible.

And they're not ice-cold sometime around 3 in the morning! They stay at around body heat, so still give the feeling of being warm.

Yep, this is a huge benefit over water bottles. I tested out both and it's nice to have water as a backup but the residual heat effect has a longer tail-off.

If you want to really spoil yourself or your partner, place the hot water bottle in bed about an hour early -- and then, just before going to sleep, refill it with fresh hot water.

I find that between the bottle itself and the surrounding sheets and mattress, a lot of heat is absorbed in that first hour. Pre-heating everything should keep the hot water bottle warm until morning. I find this to be an unreasonably effective life hack.

I wasn't aware that this was a thing that happened. I use a hot water bottle now — the typical flexible rubber one, encased in a little wooly jumper. I typically go to bed around 01:30 with the hot water bottle under the covers near my feet, and it's still warm around noon. I'm getting at least 12 hours of warmth from mine each night.

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.

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.

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.

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

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.

"...use where one would use a hot-water bottle, but without the danger of a leak."

Very interesting. Did you find any noticeable difference between the longevity of its heating as compared with water? The reason I ask is that the specific heat of water is higher than that of wheat so water should retain the heat longer.

BTW, I'm familiar with hot water bottles, they were all the rage when I was a kid before electric blankets became commonplace.

P.S.: I can't say I ever had one leak but I reckon I'd have come close. After some use, they'd start to perish around the filling point/screw stopper. The idea was to always keep an eye on it and once one noticed the first signs of perishing then not to gamble too long before replacing it.

My impression is that they don't last as long, but definitely for long enough. People think that if you need to heat them more often then it's less efficient, but if the heat doesn't last as long then almost certainly they take less energy to heat up in the first place.

It's all about transferring energy/heat from one place to another.

I've used a bunch of different pillows (cherry stone, wheat, etc) and found that, while the initial heat is great and feels better than a hot water bottle, they only stay properly hot for about five to seven minutes. Once when I had a bad back pain day, I put the microwave next to the bed so I could keep a constant reheating cycle going.

I agree. The buckwheat-filled pillows I got my kid stay warm about 10-15 minutes tops, no matter how hot I get them in the microwave.

Now, I like the idea of the microwave to reheat it, that's quite a novel idea.

Thanks for that.

We had a hot water bottle burst this week. My wife woke up to soggy feet and the water had penetrated right through the mattress. The bottle was empty and probably slowly leaking all night. It took much of the day to dry the mattress out.

On inspection we found the rubber had perished, probably as the bottle was around five years old. The replacement cost less than £10, including fluffy cover. We'll be sure to inspect this one more frequently when filling.

Not only does the bottle provide her warmth, to helps ease the pain in her arthritic feet.

One of those (or similar, I think cherry seeds) caught fire in my microwave once.

Indeed. It needs to be heated for 30 seconds, then "stirred", heating again, etc., and the temperature needs to be limited. We had one catch fire, but we patched it and it's good to go again.

I still prefer them over hot water containers. We have some that are floppy and flexible, ideal for wrapping around the back of the neck and over the shoulders.

I have one of these that has cherry stones in it. I much prefer the hot water bottle for two reasons. Firstly, I fully understand the failure mode of the hot water bottle and have rarely seen one fail; on the other hand the "cloth thing that catches fire inside the microwave" is not a failure mode I really want.

But most importantly, hot water bottles are really hot and much better at keeping me warm.

We've had more than one hot water bottle fail and it's resulted in one case in a soaked bed, which was unpleasant and difficult to deal with. I much prefer the failure mode of "catches fire in the microwave". The fire is small (and mostly just a smouldering edge of fabric), easily contained, easily put out, and the failure is easily avoided.

We've used both and settled on the wheat bag, but I recognise that other people will make other choices, and that's fine.

Never had one catch fired but definitely overdone it before and had it forever smell vaguely like burnt popcorn.

I tried to heat two rice bags at the same time once and they melted together. I didn't think about the fact that they had used synthetic fabric! I'm so used to doubling the cooking time because our microwave is only 600 watts (compared to the usual 1000-1200 watts).

I recently discovered Warmies[1] which is essentially this but inside a stuffed animal and scented with lavender and I'm not ashamed to admit that I'm low-key obsessed with them.

[1]https://warmies.com/

You can just fill a sock with dry rice and tie it off. It's cheap and easy and the hot rice smells good too.

They can certainly still leak, but the consequences are different. Instead of getting wet and risking water damage you have to sweep and vacuum wheat (or in my case rice) out of everything. Still, much less harmful to electronics and wood floors.

How about a big slug of cast iron? :)

It wouldn't play nice with water and microwave ovens. I guess you could heat it on the stove or in a regular oven instead.

Yes that's the idea

There used to be such device you’d heat up in boiling water.

it would get cold pretty quickly compared to water: https://en.wikipedia.org/wiki/Table_of_specific_heat_capacit...

I forgot about this until now - when I was a kid we had a block of cement, basically a patio stone, sitting on top of the woodstove. When I went to bed, since my room was unheated, I would wrap the cement block in cloth and put it by my feet in bed. I kind of miss that cozy feeling, but then at the same time I don't miss how cold the rest of the room was. If I woke up to a 50 degree room now I'd probably never want to get out of bed!

I find they don't keep their heat nearly as long as hot water bottles.

Why wheat? The point of using water is that it can store alot of heat.

I think they are usually husks of some type. Cheap, smell nice, conform to body, doesn't transfer heat fast enough to hurt you, and for some reason heats up in microwaves.

You can get ones with some lavender inside too - my kids love them!

Not husks - those don't have enough heat capacity. I've used ones made of corn and rice too. It's heating up the actual grain seeds, which I guess have a fair amount of water locked in the starch matrix. It always is a little steamy coming out of the microwave.

Rice works. Can just put in a sock and heat in microwave.

We made these as gifts for our parents when I was in elementary school.

You can pop a clove or two in as well to mask the rice scent.

nice idea!

If it's not dry husks but full grain, they're mostly water by weight anyway, so you get almost the same heat storage but different other properties (no leaks, slower dispersal of heat).

They are very traditional and common in Germany. I remember making them in primary school and selling at something like a "bake sale".

Also known as "magic bags" if you want to buy a premade one to put around your neck!

I’ve done this with rice. :)

Bonus points, they're shaped like cute animals and super-fuzzy. Harder to do with a water bottle. (There are covers, but who wants a soppy teddy bear?)

Negative points. I come home and think my flatmate has put a puppy in the microwave.

wait what? you mean dry bags.... ooooo

Yes ... more discussion here:

https://news.ycombinator.com/item?id=30025026

We use rice, but same idea.

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