Microwavable heating pads with organic fillers are a wonderful way to soothe sore muscles or just warm up on a cold day. Their combination of toasty warmth and good smell are a natural remedy you can enjoy every day without side effects. The rice-filled warming pad project we did here at Sew4Home is one of the most popular gift items ever featured. Most likely, it’s because they’re not only functional, they’re also really easy to make. Everybody who makes them seems to have a favorite filler. So we thought we’d do a little testing to see if we could find out which one is best.

Cotton on the outside, but what should go inside?

You can use other substrates, our original pad project featured fleece and cotton ticking, but the traditional choice for anything microwaveable is 100% cotton. It can get very warm without melting and has a nice feel against your skin. Of course, like anything you put in the microwave, even cotton will eventually burn if you cook it too long. The benefit to using the organic fillers is they require very little time to heat thoroughly, fifteen to thirty seconds is usually plenty.

But what about the filler? What should you put inside your heating pad to get the best results?

First of all, you want your filler material to be microwaveable; that eliminates anything with a metallic component, which will spark. It should stay warm for an extended period of time. It should have a nice smell or no odor when heated. And finally, it should have a nice feel against your skin. This last reason is probably why neck warmers filled with driveway gravel never caught on.

Talking with our Sew4Home team and then looking at what’s recommended on the web, we found a huge number of different fillers people have tried. The more exotic range from silica beads to cherry pits. But the ones that appear to be the most popular (and in our experience the most practical) are: rice, dried corn, and flaxseed.

All three meet the requirements of retaining heat, having a pleasant smell, and feeling good against your skin. Additionally, we like the fact you can buy any of these rather inexpensively in the bulk food section at most supermarkets. If you’re making more than a few heating pads, this is something to consider.

Some people swear by the convenience and/or cost of buying feed or seed corn at a local feed store, but there were also many concerns about “buggies” showing up in corn. We chose to use food grade fillers for all our tests and have not experienced any issues with pests – even in pads that have been used over and over for years.

We wanted to know which of our three finalists – rice, dried corn, and flaxseed – would perform best in a “highly scientific test.”

Which heating pad filler is best? Our scientific analysis.

To test our fillers we made three 5½” x 5½” test pads from scrap cotton fabric and filled each with 1½ cups of the various fillers.

We chose to compare them by volume rather than weight because that’s the limitation on your sewn warming pad.

Heat retention

Using a 1.65 kilowatt microwave, we heated each of the pads for thirty seconds. Using a food thermometer, we measured how warm the pad was right when we took it out. And then how warm it was after sitting out for five minutes.

As a reference, we heated a cup of water to 140° and found it had cooled to 124° in five minutes.

Rice: 140° out of the microwave. Five minutes later had cooled to 136°.

Dried Corn: 158° out of the microwave. Five minutes later had cooled to 142°.

Flaxseed: 144° out of the microwave. Five minutes later had cooled to 142°. This one retained the most amount of heat.

One additional plug for rice, which came in second: rice is hygroscopic, meaning it absorbs water and then releases it when it is heated. You may have put a little rice into a salt shaker to absorb the water that can invade – especially in humid climates – so the salt will shake more freely. When you use rice in your heat packs it delivers moist heat, which can be quite beneficial. Putting a small cup or bowl of water into the microwave when using any of fillers inside the heating pads can help with moisture.

Smell

We’d heard some people complain that grains, like the rice and corn, can have a cooked smell when heated. We didn’t detect any strong smell. But cooking odors may be caused when the grains are microwaved too long and burn a little.

Flaxseed is a seed and so much less prone to cook. However, of the three, the flaxseed actually had the most noticeable smell.

We often use essential oils to add a pleasant scent to our warming pads. The organic fillers tend to absorb and retain these oils, but remember that a little bit goes a long way. You need just a few drops to create a lasting aroma. Other scent options include, dried herbs, flowers, and teas.

Feel

This is the most subjective test. It really depends on the texture you like on your skin.

Rice: This has a nice “full” feel, almost like a batting fiber.

Dried Corn: It has a granular, pebble feel that’s pleasant when resting on your arm or neck.

Flaxseed: This flowed the most easily and conformed to where you laid it.

Cost

As mentioned above, we narrowed it down to our three finalists because they were so readily available from the majority of supermarkets with bulk bins. All were well under $1.00 per pound.

Rice: $.53 per pound

Dried Corn: $.96 per pound

Flaxseed: $.83 per pound

Conclusion

If you’re going solely for heat retention, use flaxseed. But all three of the fillers we tested performed better than water and so should stay warm longer than a traditional hot water bottle.

For smell and feel, we found things to like about all three. So much so, that we’ve even mixed rice and flax for some of our projects.

We now expect the major scientific journals to begin clamoring for the publishing rights to our detailed research, but you can use it for free.

Conduct your own experiment

Of course, there are many other filler options; we simply didn’t have the time to test them all. We’ve heard good anecdotal evidence for using lentils, dried soy beans, millet, birdseed, and hard wheat. Put on your white lab coat and do some testing of your own. We’d love to hear about your own successes or failures with organic fillers.

If you’re ready to put your fillers into practice, check out our projects for Rice Warming Pads, a Scented Spa Set, and a Therapy Neck Wrap. These projects also include tips on heating, cooling, and cleaning.

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123 Comments
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Nicole
Nicole
2 months ago

I also use these packs as cold packs in the freezer for kids boo boos. Actually, I use them this way more than I fo as heating pads. I wonder which has the best cold retention.

Liz Johnson
Admin
Liz Johnson
2 months ago
Reply to  Nicole

Hi Nicole – they do work well as cold packs. We didn’t test for cold retention. If you do any tests, let us know you results.

Terye
Terye
1 month ago
Reply to  Nicole

That’s what I’m wondering

David B.
David B.
3 months ago

The best thing to use as a filler is buckwheat, I know this because I invented the microwave heating pillow, in the 90s, unfortunately I didn’t patent my idea, I spent years testing different types of grain, blow-up many microwave ‘s but fond buckwheat has the most therapeutic value.

Liz Johnson
Admin
Liz Johnson
3 months ago
Reply to  David B.

Thanks for such expert input!

Amy
Amy
5 months ago

I don’t actually make the heat packs. But I am a avid user.. I have both rice and flax heat packs but just wanted to get my opinion in. I do prefer the rice filler. I feel that after a few years of use the flax seed bags tend to burn more easily even after decreasing the time in the microwave. Not sure but it may tend to burn more easily after the first initial burn. The smell it terrible. Similar to burndt popcorn. I’ve never had a problem with rice burning even with lengthy time in the microwave.

Liz Johnson
Admin
Liz Johnson
5 months ago
Reply to  Amy

Hi Amy – thank you so much for weighing in with your personal experience! As you can see, this is a very popular post – in part because of all the varying opinions.

Cathy
Cathy
6 months ago

Do I need to sew separate packets or pillows so the fill doesn’t all fall to one end of the bag or sock or is it not an issue if it’s full enough?

Liz Johnson
Admin
Liz Johnson
6 months ago
Reply to  Cathy

Hi Cathy – We do prefer to make smaller compartments. It makes it easier to mold the heating pads and place them just where you want it. Here is our most popular heating pad tutorial so you can see what we mean: https://sew4home.com/microwavable-rice-filled-heating-pads/

Shandini
Shandini
8 months ago

Can you use Mary Jane shake as a filler?

Liz Johnson
Admin
Liz Johnson
8 months ago
Reply to  Shandini

Well, that’s an unusual one — had to look it up! With anything we haven’t tested, our suggestion is always to follow our steps above to make your own small bag as a prototype to test on your own and judge your results. In general, it seems like shake might not have the density – might be too “fluffy” – to really hold the heat. But — give it a try.

Deb
Deb
8 months ago

Iam getting ready to make a neck warmer and will make a filler case out of unbleached cotton, the cover will be made like an envelope pillowcase so the filler pack can be removed and the cover washed. Like your idea of half rice, half flax

Liz Johnson
Admin
Liz Johnson
8 months ago
Reply to  Deb

Sounds like a good idea, Deb! Let us know how it turns out. Rice + flax Is one of our favorites.

Nikki
Nikki
8 months ago

Can you mix the fillers together or is it best to just do them all on there own

Liz Johnson
Admin
Liz Johnson
8 months ago
Reply to  Nikki

Hi Niki – As always, the best option is do a little test – similar to what we did above – with the mixture you’re interested in. We often use Rice mixed with Flax – especially when adding essential oil as a scent. The rice absorbs and retains the oil while the flaxseed provides a smooth, soothing texture. 

Martina
Martina
8 months ago

Is it allowed to open the bag and remove the seeds if you want to clean the bag and put back the seeds or will this spoil the seeds?

Liz Johnson
Admin
Liz Johnson
8 months ago
Reply to  Martina

Hi Martina – we have not tested this but it would likely depend on the type of filler. In general, it seems like a lot of work. When we make our pads, they are meant to simply be spot cleaned and then recycled when their life is up. You could make a cover that could be removed and washed – just remember to not use anything metal for that cover’s closure … no zippers or snaps that would not work in a microwave.

Drina Patrick
Drina Patrick
3 months ago
Reply to  Liz Johnson

HI, I make removable covers for my heat pads, easy to wash. as someone above mentioned, like a pillow slip.

Liz Johnson
Admin
Liz Johnson
3 months ago
Reply to  Drina Patrick

Yes! We offer the same slip on option for our popular Rice Heating Pads project: https://sew4home.com/microwavable-rice-filled-heating-pads/

SH07
SH07
9 months ago

What about chia seed?

Liz Johnson
Admin
Liz Johnson
9 months ago
Reply to  SH07

It’s not one of the options we tested above, and there are so many comments on this article, I honestly can’t remember if anyone has mentioned that one before. The best suggestion is to do a test similar to ours above using chia seed in a small prototype bag and see what you think about the heating ability and its retention.

Cindy
Cindy
9 months ago

Thank you for posting your “test” results. I made some of these years ago and just decided to make some again. I was looking at my recipe and wondering what my reasoning had been before I bought the ingredients again. I made mine with equal parts of rice, flaxseed, dried lavender, dried oak moss, but no essential oils. The ones we are currently using are at least five years old, maybe closer to 10 and they still smell faintly lavender, definitely pleasant. I have used spearmint and chamomile in the past as well although both of those fade faster than… Read more »

Liz Johnson
Admin
Liz Johnson
9 months ago
Reply to  Cindy

Thanks, Cindy — it’s super helpful to get your first hand experience with pads that have worked well for so long!

Jackie Lussier
Jackie Lussier
9 months ago

Has anyone ever used Groats or oat berries? My Magic Bag has oats in it by they still have the hulls on them.

Liz Johnson
Admin
Liz Johnson
9 months ago
Reply to  Jackie Lussier

Hello Jackie – we have not tested either option you describe. As you can see, there are a lot of comments on this particular article. You’d need to scroll through to find any mentions of oat berries. As always, as described above, you could make a small prototype test bag to try out and test your filler idea.

Katie
Katie
9 months ago
Reply to  Jackie Lussier

I used buckwheat groats for my brother’s heating pad. He was using it everyday multiple times a day for about 4 months. It caught fire last week. I do not think I’d use groats again.

Michele Sanders
Michele Sanders
1 year ago

I have a ton of bird seed that I am no longer going to use to feed the outdoor birds. Has anyone tried it before? One of the bags has some unshelled sunflower seeds mixed in as well.

Liz Johnson
Admin
Liz Johnson
1 year ago

Hi Michele – that is one we haven’t tested. You could certainly make a little prototype bag as we did above to test it. I just don’t know how seeds would hold up to repeated heating. They can sometimes be a bit delicate.

Annette Thomas
Annette Thomas
1 year ago

I have made my heating pads in the past with epsom salt. Great for ear infection pain but when I made it this last time I noticed that it didn’t work as well. By any chance have you mixed the salt and rice together for a heating pad?

Liz Johnson
Admin
Liz Johnson
1 year ago
Reply to  Annette Thomas

Hello Annette – so sorry, that isn’t a combo we’ve tested. Perhaps, as described above, just try a small prototype to see how it works for you.

Patricia
Patricia
1 year ago

Excellent… thank you. I’ve had experience with both rice and flaxseed; I like the idea of combining them. I’ve also added some dried lavender flowers on occasion.

Liz Johnson
Admin
Liz Johnson
1 year ago
Reply to  Patricia

Thanks, Patricia! It is one of our favorite combinations. And, although we haven’t tried dried lavender, we love using lavender essential oil for a wonderful scent.

Abigail Barrett
Abigail Barrett
1 year ago

Hii. Thanks so much for sharing. What’s the shelf life of these products?

Liz Johnson
Admin
Liz Johnson
1 year ago

Hi Abigail – Unfortunately, there’s not one solid answer for that because it depends on quantity, how “fresh” the filler might have been when first inserted, how often the bag is heated and at what temp, etc. Your best bet is usually either a “smell test” – some people detect a change in smell when it’s time to change the bag/filler and/or a heating test. If it is taking longer to heat or it is losing heat more quickly, it could be time to change.

Lorrie
Lorrie
1 year ago

Hello! I have made many bean bags filled with flax seed scenting them with dried peppermint and lavender. They were lovely gifts at first but after a while they unfortunately took on a foul rancid door and I am now emptying those I can get back from family and friends (whom I’d gifted!) and refilling them with probably rice!! So please be aware of this potential problem!!

Liz Johnson
Admin
Liz Johnson
1 year ago
Reply to  Lorrie

Hi Lorrie – Thanks for adding your experience. We haven’t run into that problem, but we do tend to blend flax seed and rice for many of our bags – perhaps that mitigates the problem. I have heard some issues with several of the fillers that are sometimes heated on a very high temp for longer periods, which also can cause them to “cook.” Thanks again for weighing in.

June
June
1 year ago

Thank you so much for conducting this experiment. I have been researching heat pack fillings for a while now and came across your discussion. I have been using a heat bag for about 15 years (not the same one) and find it so comforting for mild discomforts. I would like to start making and selling them in the uk but i think we have to comply with certain legislation. Does anyone have any info on the legalities of making/selling these heat packs in the UK please?

Liz Johnson
Admin
Liz Johnson
1 year ago
Reply to  June

Sorry, June. We don’t have any information on sales in the UK.

Tina
Tina
1 year ago

This was GREAT info! I am thinking I will mix flax and rice. What ratio of rice to flax would you recommend? I need the pillow to stay warm for at least 15 mins.

Also, how will washing the pillows affect the rice/flax? Will either grain swell (cook) changing how well it heats?

Thank you!

Liz Johnson
Admin
Liz Johnson
1 year ago
Reply to  Tina

Hi Tina – We’re glad you found us. We usually use equal amounts of rice and flax – the amounts will depend on the size of the pad. Here’s one of our neck wraps: https://sew4home.com/fast-fridays-therapy-neck-wrap-with-rice-flax-filler/ You cannot wash the entire pad; the filler will indeed swell and be ruined. It can only be spot cleaned. If you feel your pad is destined for a lot of spills and stains, it’s best to make a removable covering. Again, the project above shows this option. But, when making your covering, don’t forget that all the elements must avoid metal if you plan… Read more »

Julie
Julie
1 year ago

What rice works best? Is Jasmine rice or Long grain rice ok? And any recommended essential oils to add to rice? How many drops?

Liz Johnson
Admin
Liz Johnson
1 year ago
Reply to  Julie

Hi Julie – for the rice, just go for the most economical for you. We just tested with a standard white, long grain rice. The number of drops will depend on how much filler you are working with. A drop of two is plenty. We’ve used lavender, vanilla, and lemon – it’s really up to what you like best. Check out our heating pad project for more info:
https://sew4home.com/microwavable-rice-filled-heating-pads/

Catherine Smalley
Catherine Smalley
1 year ago

Hello, how full do you need to fill the bags? How much extra empty space do you need in the bag? Thank you!

Liz Johnson
Admin
Liz Johnson
1 year ago

Hi Catherine – there is no 100% rule for filling the pouches. It’s a bit personal preference and a bit how the pack will be used. Below are two of our project articles that show good photos of filling and finished packs:
https://sew4home.com/microwavable-rice-filled-heating-pads/
https://sew4home.com/jelly-beans-rice-filled-microwave-hand-warmers/

Tina Whitney
Tina Whitney
1 year ago

I just cut down my rosemary bush because it was getting so big, next time I will prune more vigorously. I have a pile of tender shoots and was thinking of adding a couple or three to hot packs like this. The smell of rosemary is very soothing. Does this sound like a good idea?

Liz Johnson
Admin
Liz Johnson
1 year ago
Reply to  Tina Whitney

Hi Tina — Rosemary is one of my favorites too! We’ve used dried herbs and essential oils but have not tried fresh herbs. As I usually do – I suggest making a little prototype bag and testing how well the smell works with heating and re-heating.

michelle
michelle
1 year ago

I accidently bought cracked corn, have you tried it and know if it works?

Liz Johnson
Admin
Liz Johnson
1 year ago
Reply to  michelle

Hi Michelle – No we didn’t test cracked corn. That could affect the ability to retain heat. As we often mention, the best way to tell would be to make a small prototype bag, like we did above, and test it in your own microwave to see how it performs for you in terms of heating to a good temp and retaining that temp for a length of time. If you do test, let it know how it turns out for you.

Drina Patrick
Drina Patrick
3 months ago
Reply to  Liz Johnson

Hi, yes i have used cracked corn, heats up much quicker and cools much quicker. so i swopped back to corn. but i prefer the rice.

Rochelle Michaels
Rochelle Michaels
1 year ago
Reply to  michelle

I have used cracked corn. Works great.

Liz Johnson
Admin
Liz Johnson
1 year ago

Thanks, Rochelle for letting us know!!

Amanda
Amanda
1 year ago

I have been making rice bags for several years and recently saw that the rice or corn should be replaced after 6 months-1year. I had never heard that and it seems like a lot of work and waste. What are you thoughts on replacing the filler?

Liz Johnson
Admin
Liz Johnson
1 year ago
Reply to  Amanda

Hi Amanda – there are so many stories … just here on our page – from people who have been using the same bags for 5, 10, even 20 years. I don’t think there is really ONE rule of thumb since there are so many variables in terms of type of fabric used, how often the bag is used, heating time and temp, etc. If you notice it is no longer retaining heat the way you would like or it has an unpleasant smell, replace it. Otherwise, it should be safe to continue using.

magpie
magpie
1 year ago

can i use lentils?

Liz Johnson
Admin
Liz Johnson
1 year ago
Reply to  magpie

Hi Magpie – We’ve not tested with lentils, but a visitor below did mention using split peas with good results and that would at least be similar. As we mentioned several times, the best option is always to just make a little prototype pouch, fill it with the lentils, and run the same tests as we did so see if you like the results in heating, re-heating, weight, etc.

ShamlaNaik
ShamlaNaik
1 year ago

Can we use carom seeds to make a heat pad? Carom seeds help in relieving cold and cough. Also, they are useful to relieve colic.

Liz Johnson
Admin
Liz Johnson
1 year ago
Reply to  ShamlaNaik

Hi there – we have not tested this filler, so as mentioned above, your best option is to make a small prototype pouch, fill it with the carom seeds and test how well the pouch heats, retains heat, and re-heats using the microwave. They do sound like they have some very good homeopathic features, so we’d love to hear what your tests revealed about the seeds.

Shamla
Shamla
1 year ago
Reply to  Liz Johnson

Thank you, Liz!

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