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Organic Fillers For Warming Pads: We Compare Rice, Corn and Flaxseed

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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 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 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 very inexpensively in the bulk food section at most supermarkets. If you're making more than a few heating pads, this is something to consider.

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.


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.


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.


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


If you're going solely for heat retention, use flaxseed. But all three of the fillers we tested performed better than water and so would stay warm longer than a traditional hot water bottle. For smell and feel, we found things to like about all three. 

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

Put on your white lab coat and do some testing of your own.

Make a few of our Microwaveable Rice Heating Pads and give each one a different filler. Ask your family and friends to tell you which one they like best. Then leave us a comment about what you found out.


Comments (337)

quilt fairy said:
quilt fairy's picture

I notice that no one has commented on the one great advantage that rice has as a filler:  it is hygroscopic, meaning that it absorbs water and then releases it when it is heated.  We've all put a little rice into our salt shakers to absorb the water so that the salt will "shake" freely.  When you use rice in your heat packs it delivers moist heat, which can be quite beneficial.  I have made hundreds of these as a muslin package with a removable flannel cover.  One of the additives I've used is herbal teas (just rip open the tea bag and add it to the rice), as well as mulling spices or lavender.  Dried rose petals are nice, too.

Liz Johnson.Editor.Sew4Home said:
Liz Johnson.Editor.Sew4Home's picture

@quilt fairy - Thank you for your detailed experience. You're right; moist heat is really lovely.

Kr31burns said:
Kr31burns's picture

I wouldn’t recommend using coffee beans - after heating them in the microwave at work for 20-30 seconds our office filled with smoke, the alarms went off to evacuate the building, and the fire department arrived to politely tell me to not repeat the incident. 

I would recommend putting a small cup or bowl of water into the microwave with the heating pads to help with the moisture.  

Liz Johnson.Editor.Sew4Home said:
Liz Johnson.Editor.Sew4Home's picture

@Kidium - that is a very unique filler idea that we have not tested. As mentioned above and below, with something specialized like that, a prototype test is in order. Simply make a small bag from muslin or similar, fill it with the seeds, and test the heating and retention properties exactly as we did above with our filler options. 

Ruthann said:
Ruthann's picture

I've always used feed corn and the bags last forever with a good lasting heat but wanted to share my Mother's experience when she began to make the bags she gave away most of them and they were used right away and often,  She stored her extra bags in a drawer for future gifts.  My Mom lived in Norfolk, VA which can be quite humid and hot.  When she went to get one of these bags, she found them seemingly empty, upon further examination, she found that bugs had eaten the corn or were in the corn.  To prevent this occurence from happening always heat each bag in the microwave for a minute so any hidden lives in the corn are eliminated.

Wendelin said:
Wendelin's picture

I have several bags in different sizes, some filled with cherry pits, some with seed corn and some with white rice and lavender. They are all at least 20 years old, and the coverings are 100% cotton and cotton flannel. They are heated in the microwave for 1 - 3 minutes depending on the size. Nothing has ever caught fire or smelled bad. The one with lavender still smells good when heated. I bought that one at a craft fair long ago.

My mom never used a salt bag, but when I was ill with a chest cold she would rub Vicks on my chest and heat a folded diaper in the oven for a few minutes. She would pin the diaper to my nightgown. I did the same thing for my 40 something daughter when she was little. 

We all survived. Don't worry so much.

I ran across this blog looking for the source to buy cherry pits to make a heat source for my achy arthritic hands.

Sallyrom7 said:
Sallyrom7's picture

Loved this experiment and want to make my own. Any special washing instructions?

Halcyon said:
Halcyon's picture

I noticed someone said soy beans were good to use.  Has anyone tried other beans like red beans, lima, split peas, etc.?

CeeCee7 said:
CeeCee7's picture

I used split peas once but every time I heated up the pack it smelled like split pea soup.   I have also used lentel and those work well.  Slight earthy smell, especially early on, but not really noticable after several weeks.   I still use lentils or flax depending on the feel I'm aiming for.

katie clay 27 said:
katie clay 27's picture

My favorite purchases heat wrap has flax, millet and a variety of other seeds.  It holds the heat for a very long time and I love it.  They aren't sold anymore so I'm looking to make my own.  I was wondering if anyone has tried adding coffee beans or smashed up cinnamon sticks to the base filler for an aroma boost. The Flax filler does have a distincive smell but for me the warm relaxation is more that worth it. Any feedback would be appreciated.

Liz Johnson.Editor.Sew4Home said:
Liz Johnson.Editor.Sew4Home's picture

@katie - the cinnamon sticks could certainly be an option, but their smell would be unlikely to be long-lasting. You might, as we mention above, try an essential oil in a cinnamon scent. The oil mixes in better with the filler and you need just a tiny bit for a lasting aroma.

lynda Anderson said:
lynda Anderson's picture

Hi, just wondering if I can use a soy bean for the filler of a heat bag.  I bought some and am wondering if this is okay.  My last bag had a mixure of rice, flaxseed and lentils.

Tru-C said:
Tru-C's picture

Yes, dried soy beans work well.  I made these some 15 years ago when I worked in a health food store.  We sold soy beans in bulk, they were not expensive and that is what I used in mine.  

Liz Johnson.Editor.Sew4Home said:
Liz Johnson.Editor.Sew4Home's picture

@Lynda - We did not test soy beans and so don't have an answer for you. However, as you can see, there are lots of great visitors watching this article, so perhaps someone else can pass along his/her experience with that filler option.

LAGNOCAL's picture

I just bought a 50 pound bag of dry corn from the feed store for $13.00.  Check at a feed and seed befor trying to get it in the bulk bin at the grocery store. Nearly a dollar a pound is too much.

little.y said:
little.y's picture

I work at a vet clinic and we have been looking at making some heat packs for animal use. We did have a few sample ones from a pet food company but they have eventually worn out. The problem we have is the packs must be fully cleanable. I am going to try and make the inner pouch out of a heavy plastic that can be wiped clean and disinfected and then an additional fleece outer that can be washed. I was going to use wheat but think I may try rice now.

Mama Dee said:
Mama Dee's picture

You would need to be careful with the plastic. It will melt when being heated and the chemicals will break it down fast

Joanne Robb said:
Joanne Robb's picture

Just make the pouch like normal with fleece outer.  After microwaving it wrap it up in a clean towel or washable cover and you are ready for use.  After just wash the towel or cover, reheat the pouch, wrap it back up in a clean towel or cover and you are ready for use again.  It is clean, and very easy to make.  You can bleach the towels or covers after using so they will be clean and sterile. The pouch has to be made like normal with cotton or fleece  in order to be able to microwave it. 

HML said:
HML's picture

If you make the inner lining of plastic you won't be able to microwave it.  I thought that was the whole point? 

Liz Johnson.Editor.Sew4Home said:
Liz Johnson.Editor.Sew4Home's picture

@little.y - We haven't done anything like you've described, but it sounds like all your ideas are good ones. Let us know how it turns out.

Anonymous said:
Anonymous's picture

Has anyone considered mixing materials?  A flax-rice bag, for example?  Or is that a bad idea?

Liz Johnson.Editor.Sew4Home said:
Liz Johnson.Editor.Sew4Home's picture

Others will likely weight in, but here at S4H, we did not text any mixtures. Since different fillers heat at different rates, a mixture might not be the best option for even heat

Bosco said:
Bosco 's picture

I have always used rice and it works great! HOWEVER, rice contains high levels of arsenic and I have been wondering if it could be unhealthy in heated massage bags. I looked around online and found:

"The primary routes of arsenic entry into the body are via ingestion and inhalation." 

Sooo...a steaming bag of rice could likely give off arsenic-tainted vapors I surmise and that sounds horrible. No way to test this. There are low arsenic rated rice suppliers out there like Lundberg Brand. But I think for safety purposes I will not be using rice again for massage bags. Bummer. Will look into other fillers.

SSF said:
SSF's picture

I’ve had excellent results using millet in stockinette, covered in fleece.

Oakley827 said:
Oakley827 's picture

Can you use cacked corn? I bought this for my bird feeders but the birds don't seem to like it much

Liz Johnson.Editor.Sew4Home said:
Liz Johnson.Editor.Sew4Home's picture

@Oakley827 - We haven't tested cracked corn, but it wouldn't be our first choice as there is a chance it would be more likely to degrade, and because it's all different chunks and pieces, it wouldn't be as nice and smooth as the whole grains. Do you know any folks with chickens? They love cracked corn. 

Kim G. said:
Kim G.'s picture

As a child into my teen years I watched my Aunt heat just plain salt (from the cylinder carton) in a pot on the stove stirring constantly. Just salt heated on the stove. Then she carefully poured it into a white tube sock and tied the end in a knot. we used to hold it on our ears for earaches. She had six kids. 

Reneev said:
Reneev's picture

Thank you for reminding me about this technique.  My grandmother and mom also used to do this when I was a child but I haven't  seen it for years.

Lara said:
Lara's picture

I have been using a cotton sock and rice for some time now (between 1-2 months). I think it's time to upgrade to a nice pack.

Is there a general rule how often should the grain inside (in this case rice) be swapped out? Is this necessary? I ask because I noticed that now that it's been used for a while (and we use it almost daily because our flat is very cold) it's starting to smell more. When I took a peek into the sock, it doesn't even look like rice anymore, it changed the appearance. Any suggestions?

If this is a normal thing - which one out of three can be reused the most before swapping out for a new batch or grains? 

Thanks a lot!

Liz Johnson.Editor.Sew4Home said:
Liz Johnson.Editor.Sew4Home's picture

@Lara - There is not really a general rule that we know of since there are so many variables involved. I'd go with your gut - and if you think the filler has lost its effectiveness - change it out. We have some pads that have lasted well over a year with quite regular use, but again - the conditions could be totally different from yours. This is a super popular article; there may be some helpful info further down into the comments, and I wouldn't be surprised if others weighed in with their own experiences. 

Sweeney said:
Sweeney's picture

What about wheat? I'm thinking of hard red winter wheat ? Anyone know how it would work in this capacity?

Melmerby said:
Melmerby's picture

Wheat is great for these. All mine are made of wheat and I have been using them for years. They retain heat well and don't have much of a smell. 

Bonnie said:
Bonnie 's picture

I made some with cherry pits.  I used cotton flannel.
For those who want the fleece warmth - make a separate cover, put the fleece opn after it is warmed.

My complicatrion is we do NOT use microwaves - for ANYTHING!

  So I do have a problem warming them.  Still working on the best solution.  Any suggestions?

Brenda said:
Brenda 's picture

If you don't wish to use the microwave you could put it in a roaster and put in a hot oven.

Sherry said:
Sherry 's picture

When we were kids mom would warm our aches with salt bags. Not sure if that was table salt or kosher. But the bags were in a tight weave material. (Flannel if I remember rightly) and she would put it directly on the wood burner which was never too hot, or wam it on a cookie sheet in a low temp oven. I was a kid and she's no longer around to ask, but I remember how good it felt against My chest after she would Vicks me up when I had a chest cold. Hope that helps but you will need to experiment. 

Liz Johnson.Editor.Sew4Home said:
Liz Johnson.Editor.Sew4Home's picture

@Sherry - Thanks for adding your suggestion - and such a great story!

tim said:
tim's picture

Yes Bonnie and everyone who asked, I do have a quality suggestion, I use it myself: If you can't or won't use a microwave, get an evacuated glass tube from China (lol), that's a double borosilicate glass with a near-vacuum between. Lay it out in the sun during the day (you don't absolutely need clear sun, but on overcast days it is slow). Put your favorite (long and rather thin) hotsack inside, even metal filling no problem here. My large solar cooker gets it to over 150C in a good two hours with clear sun, and that's all free heating. We live offgrid, and although we could use a microwave I haven't yet: too much drain on batteries. Nothing is nicer than taking a hot oven inside a cold house :-)

If you need pics, or seek inspiration, our offgrid story is on mygermanshepherd.org under tiny house large dog. I am a bit behind with photos of the recent happenings though. It's too cold to edit.

Sarah M. said:
Sarah M.'s picture

What about using a crock pot?  Ball up some aluminum foil in the bottom to keep the bags off the bottom and turn the crock pot onto low - keep in until they are the temperature you prefer.  Also, if you have a woodstove, you could do something similar (adding water to the bottom of the pot will give you a moist heat) and you could always have one at the ready - you would just have to wait a few minutes for it to cool enough to use.

Autumn1975 said:
Autumn1975's picture

I also do not use a microwave. Although i have only used rice in a sock, hence why I'm hear looking for something more durable. In the past I have just put my rice sock in a pie pan or on a cookie sheet that has been preheated. Oven temp and time will vary. Experiment. But as i was reading your comment i also though maybe a double boiler would work to?

VickiS said:
VickiS's picture

If it's a heat pack that you've already used, it could be rice. I made my own heat packs with rice some time ago and have just had a hole appear in one from being loved way too much, and the rice inside now resembles small white granuals. I have been making rice packs for myself for years and love them.

Judy Kay said:
Judy Kay's picture

I just took an old heat wrap apart and it had some kind of tiny white granuels in it, looks about the size of bird food or smaller. Does anyone have any idea what they can be and where I could find them. I want to make some for Christmas gifts.  All the information I have read has been extremely helpful and I want to send a big huge THANKS to everyone who has posted ideas and information.

Tiffany Roundy said:
Tiffany Roundy's picture

It may be millet. It is a grain that is round and looks like bird seed

Liz Johnson.Editor.Sew4Home said:
Liz Johnson.Editor.Sew4Home's picture

@Judy - It's hard to tell, but it sounds like something that isn't an organic filler. We didn't test any non-organic heating beads. Perhaps someone else in our visitor universe may recognize what you've described. 

Maya Tasa said:
Maya Tasa's picture

Hi. I love the idea of making a heat pack myself. Can i use a used cotton t-shirt,cut to size, for this? 

Toi said:
Toi's picture

hi, has anyone ever used


Hi, has anyone tried beach variety sand to fill bags instead of rice?

Anonymous said:
Anonymous's picture

I started this comment thinking I could be definitive about the safety and feasibility of heating dry sand in the microwave, but it's actually a bit contentious.

Mostly, if you're going to put sand in your microwave, make sure there's not metal in it, and if the sand isn't getting warm, cease, because running the microwave with nothing to absorb the radiation is bad for the magnatron.

The reason for the debate is that microwave ovens work by exciting dipoles: molecules like water that have a positive and negative pole. Sand molecules are slightly dipole, but are also locked in crystaline structures, which limits their ability to move and absorb the microwave radiation.