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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Michele Sanders
Michele Sanders
9 days 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
9 days 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
13 days 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
13 days 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
29 days 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
28 days 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
4 months ago

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

Liz Johnson
Admin
Liz Johnson
4 months 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
4 months 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
4 months 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
5 months 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
5 months ago
Reply to  June

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

Tina
Tina
5 months 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
5 months 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
5 months 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
5 months 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
6 months 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
6 months 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
6 months 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
6 months 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
6 months ago

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

Liz Johnson
Admin
Liz Johnson
6 months 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.

Rochelle Michaels
Rochelle Michaels
6 months ago
Reply to  michelle

I have used cracked corn. Works great.

Liz Johnson
Admin
Liz Johnson
6 months ago

Thanks, Rochelle for letting us know!!

Amanda
Amanda
7 months 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
7 months 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
7 months ago

can i use lentils?

Liz Johnson
Admin
Liz Johnson
7 months 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
7 months 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
7 months 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
7 months ago
Reply to  Liz Johnson

Thank you, Liz!

Nancy
Nancy
7 months ago

I have made these for many years using rice, but I use flaxseed now. I see a natural doctor and as per testing I had a Mercury toxicity! I could find no reason for the Mercury,. then I remembered something about rice, I researched and found that rice has mercury in it and I had been heating my heat pack up every couple hours, every night! It certainly made me think twice about the rice! As per my doctor I detoxed. Mercury is very dangerous in the body that is why I have no silver fillings in my mouth! I… Read more »

Sandra Carne
Sandra Carne
5 months ago
Reply to  Nancy

That’s good to know. I am making my mum who is 99 this year a couple of bags to warm her hands. I am making them with a Border Collie material, I will put flaxseed in them. I bought her one years ago and it’s worn out. I have a Border Collie called Boris and she loves him. I did have a Border Collie for 17 yrs called Kelly, she called her bag Kelly, this time it will be Boris . Thank you so much.
Sandra Carne

Liz Johnson
Admin
Liz Johnson
5 months ago
Reply to  Sandra Carne

Hi Sandra – what a lovely story! If you follow us on social media, we’d love to see a picture of your mum with her new Boris bag :-).

Jneeta
Jneeta
7 months ago

So I have a silly question to ask about the dried corn seed. Is this seed thats found in the bins at the store the kind thats used for popping corn…or how is it different? Thks.

Liz Johnson
Admin
Liz Johnson
7 months ago
Reply to  Jneeta

Hi Jneeta — There is a difference. You don’t want popcorn, you want dried seed corn or feed corn. Depending on the area in which you live, you may have to go to a feed store or similar rather than a grocery story to find it. Here’s a good article from the folks at the Nebraska Corn Board:
https://nebraskacorn.gov/issues-initiatives/your-food/field-corn-vs-food-corn/

Lovisa
Lovisa
7 months ago

Oh! Forgot to ask ~ How much lavender bud in relation to flax/rice mix?

Liz Johnson
Admin
Liz Johnson
7 months ago
Reply to  Lovisa

Hi again – That is a matter of size of the heating pad and personal preference as to how much of the lavender smell you want. For example, for these sachets, we use about 1/2 to 3/4 cup for each. We also often use essential oils, in that case using just a couple drops per cup of rice/flaxseed mixture. As mentioned above, making a small test bag would be a good way to determine if you like the scent.

Lovisa
Lovisa
7 months ago
Reply to  Liz Johnson

Thank you so much for this input. Making a test bag as you suggest will be most helpful in getting the proportions right. My original pad is 11.5 inches wide, 18 inches long, and weighs a little over 3 lbs. Calculating the proper amounts is going to be an interesting challenge! The designer stitched across the pad to create separate panel segments that kept the contents evenly distributed so I plan to duplicate her design. I emptied one of the panels to get a better idea of proportions she used and it looks like around 85% flax and 15% rice.… Read more »

Liz Johnson
Admin
Liz Johnson
7 months ago
Reply to  Lovisa

Let us know how it turns out. In addition, we do have a warming pad tutorial If you want to take a look at ours: https://sew4home.com/microwavable-rice-filled-heating-pads/

Lovisa
Lovisa
7 months ago

After an unfortunate incident involving a sick pet, I am finally forced to make a new heating pad to replace one that has functioned well for 20 years (no, 20 is not a typo. It really did last that long although its slipcover looks as though it’s seen wartime combat). It contains a mixture of whole flax seeds and what appears to be jasmine rice. I’m guessing a 50-50 split. The original instructions advised heating no more than 2 min 30 sec which seems a little long compared to most recommendations but never once did it burn or emit any… Read more »

Liz Johnson
Admin
Liz Johnson
7 months ago
Reply to  Lovisa

Hi Lovisa – Wow – 20 years is pretty impressive. Thanks for posting your input.

Tam
Tam
8 months ago

Where can you purchase these things in bulk because I cannot find anything close to a dollar a lb for flaxseed.

Liz Johnson
Admin
Liz Johnson
8 months ago
Reply to  Tam

Hi Tam — we shopped at a local warehouse store, but have also seen them at most health food stores and organic grocers. That said, this version of the post went up in 2018 – so it’s likely prices have gone up. I took just a super quick look at options on Google, and it does look like, on average, smaller quantities are now closer to $2/lb. You have to get into larger bulk quantities, like 10lb + to be closer to $1/lb.

Doreen Chindezwa
Doreen Chindezwa
8 months ago

In process of making my own heat caps for deep conditioning my hair and wanted to know what the best filler is. Thank you sew4home for doing the legwork for us. Will definitely be going for flaxseed as heat retention is the main property
I am looking for. Thanks for a great job and happy new year to all.

Liz Johnson
Admin
Liz Johnson
8 months ago

Hi Doreen – Sounds like you have a plan! Let us know how it turns out.

Tina
Tina
5 months ago

Last edited 5 months ago by Tina
Kelly Dannemann
Kelly Dannemann
9 months ago

Love all your educational Tutorials, Thank you for taking the time to make this article.

Margie Smith
Margie Smith
9 months ago

HI there I have been using the same whole corn heating bag for several years. I’ve changed out the fabric three times. Still holding the heat well. I like the weight of corn on my neck it helps keep my neck and shoulders down. I also take to bed under the covers keep my warm colder nights. In the morning it’s still warm. Love my corn bag.

Liz Johnson
Liz Johnson
9 months ago
Reply to  Margie Smith

Hi Margie – thank you so much for weighing in with your experience! It’s super helpful for others to read all the feedback.

kim
kim
9 months ago

Has anyone compared these to buckwheat hulls? I have an old, well-loved microwavable heating pad stuffed with buckwheat hulls. I’d like to make a new one, but when searching came across an article that said they would burn when heated. I can attest to that not being the case. I have had that happen with rice-filled hand warmers and the smell isn’t pleasant.

Liz Johnson
Admin
Liz Johnson
9 months ago
Reply to  kim

Hi Kim — you do have to be careful with the little hand warmers – they have much less rice in them so the heating time definitely needs to be kept low. We haven’t tested the buckwheat hulls, but have heard from others that it works well – and if you already have used them with success, I’d say go with your own positive experience over someone who might have heated too long or on too high a setting.

Diane
Diane
9 months ago

Can I mix rice and corn

Liz Johnson
Admin
Liz Johnson
9 months ago
Reply to  Diane

We’ve mixed flax and rice because their textures are similar but have not experimented with a rice and corn mixture. It seems like it might not feel as “smooth” as if the filler is all the same approximate size. But – as we mention, the very best option is to do your own little test by making a small pouch as we describe above. If you do, let us know what you discover.

Janet
Janet
9 months ago

Hi Thanks for sharing, have you checked how long is the shelf life of flax seed as fillers for warming pads? and where should I store my warming pads with flax seeds? TIA!

Liz Johnson
Admin
Liz Johnson
9 months ago
Reply to  Janet

Hi Janet –  It’s hard to give a definitive timeline for a change-out since there are so many variables in terms of amount of use, length of time heated, size of the bag, fabrics used, etc. We had one visitor mention a bag she’s used for 10 years! In general, it’s probably best to simply give yourself a time frame you feel comfortable with. Freshening the bags is also a good way to make sure the fabric looks clean and crisp since washing isn’t really an option.

kim
kim
9 months ago
Reply to  Liz Johnson

I’m planning on making a warming pad with a removable cover that can be washed regularly.

Liz Johnson
Admin
Liz Johnson
9 months ago
Reply to  kim

Let us know how it turns out. Remember to use something like an envelope closure or another microwave-safe solution.

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