Instructables
After watching my mom and sister spend $12 a pop on those store-bought disposable heat pads and around $30 or more on various gimicky microwaveable reusable ones, I stumbled upon this idea while marveling at how MUCH pee my nephew's diaper held.

A bag of 40 diapers costs about $10, so you will be spending about $.25 each. You can reuse these a couple dozen times easily, so figure on a penny per use (not including any energy cost for running your microwave, of course). Not bad, when compared to the $12 for one or two single-use disposable hot pads at the drugstore. These retain thir heat for a couple hours.
 
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Step 1: What you need:

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A clean, dry disposable diaper and a good sturdy freezer bag.

Step 2: Open the diaper.

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Open up the diaper and spread it out so it is like a cradle.

Step 3: Fill with water.

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Take the disposable diaper (preferably clean) and run it under water, pouring the water into the hammock-like center until it is puffy and full. If you are interested and/or obsessively inclined you can measure one cup at a time. I found three cups is perfect for my nephew's size 4 Kirkland diapers, I doubt there is much variation needed.

Whichever method you use, try to get the water absorbed to all edges and press it around a bit so that it is nice and puffy end-to-end.

Step 4: Enclose in freezer bag.

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Next get a gallon-sized heavy-duty freezer zip bag and position the diaper neatly at the bottom. Squish it around to make it perfect if you want to. I do.

I fold the outer edges inward to form a neat tubish rectangle and then stuff it into the bottom of the freezer bag. Again, squeeze it around and work it into the shape of the bag.

Step 5: Heat it up!

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Now place it in the microwave for about three minutes and thirty-three seconds (depending upon your microwave's power). Make sure to leave the bag partially unzipped or it might explode. Be careful while removing it, the heat can sneak up on you in spots!
HattieD3 months ago

Genius! am going to try this. It just so happens we have disposables on hand.

NetWt4Lbs6 months ago
My mom actually did this when my brothers were newborn, I used this method a couple times myself and it is fantastic
I love this! I'm using it as we speak! I thik I have acute sinusitis and since its the weekend the doctors office is closed, so I started looking up moist heat packs for home remedies and I came across this! It is really helping with my pressure and tooth aches! Thank you for sharing!
Dalya6 years ago
Can I use a disposable pad? Well they are almost the same thing..but I'm wondering.
rupamagic (author)  Dalya6 years ago
You know, I'm not absolutely certain, but I don't think feminine hygiene pads have the same weird gel inside that diapers do. After all, I can't think of any pad that would (or should) hold anywhere close to three cups of liquid! Also they are a lot smaller that the average diaper so they wouldn't cover as much area, but hey, a pad might be just perfect for one of those cold eye masks for when you have a headache, hangover or just puffy eyes! Why don't you give it a try and report back. You've got nothing to lose but a disposable pad, after all. You can use the freezer bad again with a diaper if it doesn't work. Cheers! Rupa
They actually do have gel. I learned this just recently when my water broke! Also, you can just buy the gel alone in most garden centers. It is called soil moist. The container may not look big, but it only takes a very small amount to puff up a LOT! I made neck coolers with these that just tie around like a necklace. For that project I only use 2 tsp. of the granules and it fills up the cloth. You can soak them in cool water and it keeps you cool while you work outdoors in the summer.
Phixius Phixius4 years ago
Well, I'm going to go ahead and point out, even though this was over a year ago now, that this comment was made by my wife who apparently didn't realize she was logged in as me. My water has never broke. I don't even have a "water".
Dalya rupamagic6 years ago
Disposable pads do have the same gel inside. It's like a powder at first, but then it turns into gel when wet. It's a very weird and toxic material. Some babies are even allergic to disposables, then they have to use cloth diapers. Heck, it's why a lot of women now converted to cloth menstrual pads. Lol. I'm one of those converts. heh! Thanks, I'll see if I can try :D
jauncourt Dalya5 years ago
Actually, babies are often allergic not to the gel but to the the scents used to cover the plastic smell of the shell material, or their skin is irritated by the "clothlike" material or by the non-breathability of the plastic shell materials.

The gel is really benign ... unless you eat or inhale it. Even skin-to-gel direct exposure does nothing more than dry the skin slightly. It eventually breaks down in normal environmental conditions, but the shells of these items (both the spun "cloth" material and the nonpermeable plastic barrier) do not.

Most women I know who have chosen to use cloth for babies or themselves have done so for environmental and cost reasons, because disposable options are both expensive and wasteful. These are much more compelling reasons to me that scaremongering about the absorptive material.
I have surgery coming up. I know I'll be in pain. I'm going to try theidea in the cold form. clever Idea. thanks for sharing. Well done
AzureEyes5 years ago
I'm curious to know if you can reuse these, i would imagine up to a certain point, and yes considering that it would take a while for these to decompose, on another instructable is that you can take the filling out and put them into potted plants to help retain the water in the pot and use less water to keep it moist. : D there you have it...lots of ways to save money.
brabantia6 years ago
Cunning plan! I've been looking for something less silly than the gadgets your mom fell for. I'm a bit concerned about using diapers though, it seems they take decades to decompose ...
You can also use rice to accomplish the same goal... in fact, I think I'm going to instructable that tonight! Keep an eye out!
rupamagic (author)  sarahfish5 years ago
Yes, a lot of people use rice or millet or flax, which I did for years with decent results. The reason I shared this was that I find this lasts longer and is a bit more comfortable because it is "smooshy-gushy" and soft, as opposed to the grains which all tend to fall down and lump in the lowest point of the sack. I look forward to your instructable!
aklyatne5 years ago
The gel inside of disposable diapers is a kind of polymer that absorbs the water and then expands, forming a gel. Water does have a high specific heat capacity, but it's not the highest - not by a long shot. When heated, the water inside the gel heats up and the polymer insulates the water and keeps the heat in for a longer time - a side effect of this is that it keeps the gel at a decent temperature for a long time, and it's harder to burn yourself with it. It's close to the same as what commercial ice/heat packs do, but it evaporates, which is why it's a lot cheaper and less widely used.
issaandbri5 years ago
Can this be reused? If you let it dry out can you wet the gel again?
rupamagic (author)  issaandbri5 years ago
Sure, we use the same one for months. I actually keep one in the fridge as a cold pack and then if hot is needed just pop it in the micro.
worldhq1016 years ago
Hey Ms Rupa, what a clever idea ! I have lower back pain a lot and this seems to be just what I need ! You could use this same technique for a cold compress as well couldn't you ? . . . maybe use refrigerator instead of the freezer to keep them pliable. Whq101
I used to be a homebirth midwife, and we would have our clients soak a few large menstrual pads in water and freeze them in a "cupped" shape to use as icepacks perfectly suited to what they needed them for. This worked great and we got lots of thank-yous for the suggestion. Since diapers and most disposable pads have the same gel filling, it should work just as well. They do freeze pretty hard, but leaving it out on the countertop for a little while softens it up enough to be comfortable.
Yes this is an excellent way to make ice packs also. The technique is basically the same except that I use 1 cup distilled water, 1 cup denatured alcohol, and 1 cup liquid dish soap. Freeze instead of microwave. The alcohol and dish soap keep the contents nice and pliable even after being frozen. Stays cold much longer too.
rupamagic (author)  safyrmwn6 years ago
Awesome, thanks for the tip!
rupamagic (author)  worldhq1016 years ago
Hello Miss HQ, good to hear from you! You bet it could be used for cold, I haven't tested the cold action much, it does freeze solid but in the fridge could be about right! You be sure to report back if you try it and let us know!
iq_abyss6 years ago
Someone aught to put some of this gel in a calorimiter and find it's specific heat (I'm guessing it will be above °C = 4.186 Julie/gram). It would be interesting to see the data (analyzed as well as raw.---I don't have the equipment otherwise I'd do it myself and post the data.....(I wish I had some funding :-(
Cool! Thats a great idea! Well done. Kind of like a hot water bottle.
rupamagic (author)  joejoerowley6 years ago
Precisely! Only the gel in the diaper seems to stay hot a LOT longer than the water in a rubber bottle does, so if you are lazy or in a lot of pain it means less trips to reheat it.
Thats interesting, water has one of the highest specific heats around.
rupamagic (author)  joejoerowley6 years ago
Yeah, go figure. Maybe one of these science smarty-pants can explain it? I mean, it's still the water that is hot, so I am guessing the gel is just acting as an insulator? Whatever the science behind it, it is the same concept as that blue ice, and after some experiments, yes, it also works as a freezer-pack for coolers (or transporting severed body parts), because it stays frozen longer than the freezer bag full of frozen water alone. Unfortunately it freezes rock solid so not particularly comfortable as a cold pack.
Actually a smart idea. Very nicely done Instructable.
rupamagic (author)  GorillazMiko6 years ago
Thanks! Let me know how you like it (if you have a chance to utilize it).