Top 10 Fillers for Microwavable Heating Pads

If you have menstrual cramps, arthritis, or other pains you may have heard about the wonderful natural pain relief that heating pads offer. However, when you look online at all of the different options and DIY tutorials, you may find yourself asking...

What heating pad is the best?

The best heating pads are those with fillers that can retain heat for long periods of time, are durable, comfortable, don't smell bad after repeated use, and are easy to find. 

Despite how cute a heating pad may appear, the cover isn't indicative of the quality of the heating pad.

As with people, its what's on the inside that counts, especially when it comes to finding relief.

It is important to find a heating pad with quality filling.

I decided to do some research and a little experiment to determine what heating pad filler was the best.

The results were surprising.

Ten different heat pad fillers in white bowls

10 Best Heating Pad Fillers

  1. Lava Sand
  2. Flax Seed
  3. Walnut Shells
  4. Wheat Berries
  5. Pearl Barley
  6. Steel-Cut Oats
  7. Corn Kernels
  8. Rice
  9. Cherry Pits
  10. Clay Beads

What Makes The Best Heating Pad Fillers

When I set out to find the best heating pad filler, I made a list of everything that I was looking for in a heating pad, and asked the following questions:

  • Heat Retention: How hot does a filler get and how long does the heat last?
  • Durability: Is the filler able to withstand multiple heating and not burn or spoil?
  • Comfort: Does the filler give the pressure that helps with pain relief?
  • Availability/Cost: Can I easily find the filler and is it affordable?
  • Smell: What does the filler smell like after being heated?


The Heating Pad Experiment

In order to test the different fillers, I went out and purchased each of the different fillers.

Then I began the experiment.

First, I then placed 1 cup of the various fillers in individual yet similar microwaveable bowls.

Second, I examined the contents for mold, bugs, and other impurities in the products.

Third, I heated up each bowl individually in my standard 1200 watt microwave along with a mug full of water for the average the recommended time of 1 1/2 minutes (as well as 3 minutes for the rock based fillers lava sand and clay beads).

(It is recommended to place a cup of water in the microwave when warming up any heating pad or heating pad filler to avoid burning and possible combustion.)

Fourth, I noticed the smell when it was heating and afterwards.

Fifth, I measured the temperature of each filler by running my hand through the fillers to gage the temperature on and below the heated surface of the materials.

Sixth, I recorded the temperature of each filler at different intervals, including room temperature heat, when it initially left the microwave, one minute after leaving the microwave, five minutes after leaving the microwave, and continued in five minute increments up to thirty minutes.

Seventh, each filler was placed in a plastic bag to see how it would contour and offer relieving pressure to the body.

Heat Scale

I initially planned on using a thermometer to check the exact temperatures of the fillers.

Unfortunately, each time I tried to take the temperature of a filler right out of the microwave, it was too high for a standard thermometer to gauge.

So instead, I decided to come up with a scale that was more relevant to the situation.

That scale was was based on how comfortable it was to the touch.

(I don't recommend doing this at home since some of the fillers were burning to the touch, but that was the small price to pay in the name of science.)

I categorized temperatures as followed:

  • Burning, too hot to the touch
  • Uncomfortably hot
  • Comfortable heat (Ideal)
  •  Warm
  • Slightly Warm
  • Cool/ Original Temperature

The Results of the Heating Pad Experiment

Below is a chart of how long the different fillers had detectable heat.

Chart showing heat retention in heat pad fillers

What this chart doesn't show is the fluctuation in temperatures between the different heating pad fillers.

However, that as well as the other judging criteria helped determine the ranking of the best heating pad fillers. 

#1 The Best Heating Pad Filler is Lava Sand

small pile of lava sand

After taking into consideration all of the different criteria for the best heating pad filling, lava sand came out as the clear winner.

What is Lava Sand

Lava sand is legally mined sand made when volcanic molten lava met the ancient sea. 

It is a form of basalt which is known for its ability to absorb and retain heat.

Why Lava Sand is the Best Heating Pad Filler

When comparing lava sand to the other heating pad fillers, it came out on top in every category.

Although this filler is relatively unheard of in the world of heating pads, it is the best when it comes to retaining heat, durability, comfort, overall affordability, and smell.

Heat Retention

When it came to heat retention, lava sand was the clear winner.

Although it can retain heat as long as other fillers such as rice, corn, wheat, and oats, lava sand didn't burn me when I ran my fingers through it when it first came out of the microwave.

However, it was warm enough and to provide the heat therapy that people are looking for when they use heating pads.

That translates to a heating pad that you can use immediately that is warm enough to provide relief without having to wait for it to cool to a comfortable temperature.

Not only was it not excessively hot when it left the microwave, but it kept a constant temperature longer than all of the other heating pad fillers.

That means if you are suffering from any pains you won't have to make as many trips to the microwave to reheat the heating pad as you would with other heating pad fillers.

*It should be noted that the results for lava sand are based on a 3 minute heating period.

This was done because there was no chance of burning unlike other fillers using that time frame.

When heated at the 1 1/2 duration, lava sand was not hot enough to properly compare with the other fillers.


When I had opened bags of some of the food stuff used as heating pad fillers, I was grossed out by what I saw.

Mold, bugs, rot...it was disgusting.

Lava sand didn't have any of those problems.

Since lava sand is a mineral, it doesn't ever go bad or attract creepy crawlies.

And as mentioned earlier, it doesn't burn, making lava sand the perfect filler to be heated over and over and over again.


Another great thing about lava sand was that it was heavy.

Now, that might not sound like a selling point to most people, but for me it is crucial.

When I am having menstrual cramping or other pain that requires a certain amount of pressure to help relieve it, the heavier the heating pad the better.

However, I don't want something overly bulky, which is where the density of the lava sand comes in very handy.

Its weight gives just the right amount of pressure I need to get the best relief a heat pad can provide.

Also, since it is sand it can contour around different parts of the body without being bumpy and lumpy.

Availability and Cost

Although the initial cost of lava sand may seem high compared to the other heating pad fillers on this list, when you calculate it's lifetime value, it actually ends up being one of the cheaper options.

You may ask, "How can it be cheaper when I can get a bag of rice for a fraction of the cost?"

The key words here are LIFETIME and VALUE.

Unlike most of the other heating pad fillers, lava sand is never going to expire, go stale, attract bugs, etc. like most of the heating pad fillers made of pantry items and food stuffs.

All of the other heating pad fillers with the exception of clay beads are perishable and will eventually need to be replaced.

If you were to replace the rice in your rice sock every 3-6 months, and calculate the rising cost of food, you would eventually spend more on the rice sock than on lava sand.

Not to mention you will never have to worry about lava sand burning or combusting when you heat it up.

When it comes to availability, at the time of the writing of this article lava sand is exclusively available on Lavahq.com.

With one click, you can get your very own lava sand heating pack.

*One thing to note, although the sand will last forever, the durable cover may need to be replaced on occasion.


As mentioned before, since lava sand is non perishable and able to be heated several times without burning lava sand does not smell.

#2 Flax Seed

white bowl of flax seed

As the name denotes, flax seed are seeds from the flax plant.

Out of all the fillers made out of perishable food stuffs, flax seed out performed in several key areas.

Heat Retention

Although flax seed did not maintain a detectable heat as long as thicker kernelled fillers such as wheat, corn, or barley, it didn't burn me when it first came out of the microwave.

It also was able to maintain a usable consistent heat earlier and longer than other perishable fillers.


After several times of heating the flax seed, I did not notice any burning or smell emitting from it.

However, having had flax seed in my pantry before I know that it is susceptible to weevils and other cupboard pests.


Because of the small size of the flax seeds, they were able to contour to different parts of the body.

Although not as heavy as the lava sand, flax seed did offer some weight and pressure when used.


Flax seed was one of the pricier of the food stuff heat pad fillers.

However, it was still affordable, with a one pound bag listing under $6 online.

Flax seed can even be purchased at local grocery stores and health food stores, making it very easy to find.


When heated, I did not notice any smell. However, after repeated heating the seeds may begin to burn, especially since it is such a small grained substance and will need to be replaced periodically.

#3 Walnut Shells

white bowl of walnut shells

Walnut shells are the pulverized shells of walnuts that are packaged and sold for use in reptile and bird habitats.

Heat Retention

When initially heated up, walnut shells were a little too hot to touch, but not burning hot like other fillers.

It cooled enough to be usable fairly quickly and was able to maintain a useful amount of heat for about ten minutes.


Because of the dark coloring and woody substance of the shells, I didn't notice any detectable burning after heating it several times.

Also, since it isn't technically a food stuff, it shouldn't rot or attract bugs if left in a cool dry location.


Because walnut shells are generally pulverized to small pieces, a heating pad filled with it will contour to the body and provide pressure.

It is denser and heavier than flax seed, but not quite as heavy as lava sand.

Availability and Cost

When I was researching walnut shells as a possible heating pad filler I saw many places mention that a bag of it could be found in most local pet stores.

In the pet industry, walnut shells are use as an organic bedding for reptiles and birds and can be generally purchased in large bags.

However, when I went to various large pet stores, I was unable to find any.

I then turned to the internet and found a seven pound bag of it for about $10. 

However, either because of the initial condition of the bag or the rough handling of it while in transit, the package arrived with a large tear and leaked everywhere.


The walnut shells themselves have an earthy odor and smell like walnuts, not necessarily pleasant, but not necessarily bad.

When heated, the smell didn't really increase.

#4 Wheat Berries

white bowl of wheat berries

Wheat berries are wheat that hasn't been processed except for the removal of the outer hull which allows it to last longer and is a staple in long term food storage.

Heat Retention

Wheat berries were one of the best fillers when it came to retaining heat.

However, when it first came out of the microwave it was very, very, very, hot.

If I was to use it as a heating pad, it would still probably be too hot even if a fabric barrier such as a dish towel or blanket was used.

It took about 5 minutes for it to cool down enough to be used.

With that said, once it did cool down it was able to maintain a useable heat for at least 15 minutes.


Because of the dense and dark nature of the wheat berries, it was able to be reheated several times without burning too much.

Since the wheat berries I used had been in a vacuum sealed can, there were no bugs, rot, or other initial issues with the wheat.

However, experience has proved that once wheat berries are exposed to moisture in the atmosphere and fluctuating temperatures, it can begin to go bad and rot.


The overall comfort level of the wheat berry heating pads wasn't too bad, but it didn't contour as nicely as the smaller grained heating pads.

It provided adequate weight and pressure to make a decent heating pad.

Availability and Cost

For some reason, wheat berries in general are not easy to find in a grocery store unless you look for things in the long term food storage sections.

They are generally found in metal cans and can last up to thirty years when left unopened and stored in cool dark places.

Also known as hard wheat, red wheat berries, and hard white wheat berries, cans of wheat can be purchased online and in bulk.


Wheat berries have a faint earthy smell which doesn't increase unless overheated and burnt.

#5 Pearl Barley

white bowl of pearl barley

Pearl barley are barley grains with the outer hull and some of the bran removed.

Heat Retention

Because pearl barley and wheat berries are similar in size and texture, both performed similarly in every test.

As with the wheat berries, the pearl barley was initially way too hot to touch, but after five minutes ended up being a hot, but comfortable temperature and retained detectable heat for over 25 minutes.


Unlike wheat, which I was able to find in a vacuum sealed container, I found loose grained barley in a bag which was susceptible to bugs and other pests.

Pearl barley was also a lighter color which browned slightly after being heated repeatedly.


The smaller grained barley was similar to wheat with providing comfortable contouring and weight needed for a heating pad.

Availability and Cost

I purchased the pearl barley from a local health food store for about a dollar for a small bag.

It is also available in larger quantities in stores and online, so it is fairly inexpensive and easy to purchase.


Pearl barley doesn't have much of a smell when not heated. 

However being repeatedly heated the barley will begin to smell if it begins to burn.

#6 Steel-Cut Oats

white bowl of steel-cut oats

Steel-cut oats or Irish oats are groats (hulled kernels of cereal grains) that are chopped into pieces instead of rolled out and flattened like traditional oatmeal.

Heat Retention

When first removed from the microwave, steel-cut oats were hot and uncomfortable to the touch.

Although it did retain heat fairly well, it didn't retain it as well as walnut shells, pearl barley, or wheat.


Because it is a processed grain, steel-cut oats do spoil faster than unprocessed grains such as wheat berries.

It heated well without burning, but grew darker with each heating session.


Because it is cut into smaller pieces than barley or wheat, steel-cut oats offer more contour to the body while still providing adequate weight for a heating pad.

Availability and Cost

At the local health food store, I was able to find a small bag of steel-cut oats near where they keep the large buckets of loose grains.

The bag cost be about $1, with larger quantities available in most breakfast aisles at the store or online.


The steel-cut oats smelled like traditional oatmeal, with the smell intensifying as it was heated up.

#7 Corn Kernels

white bowl of dried whole corn

Corn kernels are dried corn, however it is not the same corn variety as popcorn.

What Kind of Corn for Heating Pads

The best type of corn to use is whole corn which is generally used as bird food or animal feed.

If you have ever had to suffer through the stench of burnt popcorn, you know that a special kind of corn is needed when making heating pads.

Whole corn is like the corn that you would eat off of the cob, only dried out.

Heat Retention

Although dried corn is one of the main fillers of choice for DIY heating pads, I found that it performed poorly when compared to other heating pad fillers.

The main issue was how hot it was when it first came out of the microwave and how long it took to cool down to a usable temperature.

Out of all of the fillers, it had the shortest time of usable heat.


Another reason why dried whole corn is low on the list was the condition that the initial corn kernels were in when I first put them in the bowl.

The kernels themselves were not the best quality, with several showing signs of deformity, rot, and mold before they had dried.

When it came to heating, corn did alright.

However, the more it was heated, the darker the color of the corn became.


Because of the large size of the individual corn pieces, the bag of corn did not contour as easily as the other heating pad fillers.

It was lumpy and it was bumpy and was bulkier than other fillers.

Needless to say, I wasn't very impressed.

Availability and Cost

As common as corn is, finding dried whole corn at a reasonable price was surprisingly difficult.

Normally, dried corn is not found in grocery stores, but is mainly found in pet stores.

However, when I went to check out various pet food stores or pet food sections of stores, I was unable to find a bag of only dried corn.

They had corn mixed with various other seeds, but not plain corn.

When I looked online, I found bags of dried corn, but they were very large and very expensive.

I finally found a five pound bag at a local feed store that had an aisle for pet birds.

The bag itself cost me about $6, but as I mentioned before, when I opened it up I found that the corn itself was a very low quality.


Before it was heated, the corn had a faint dusty corn on the cob smell.

The smell did not really increase when heated initially, but increased in smell the more it was heated.

#8 Rice

white bowl of unheated long grain white ricewhite bowl of heated long grain white rice

Although rice is the most popular food stuff when it comes to making a heating pad, I found it to be the least impressive.

The following results are based on using standard long grained white rice.

Heat Retention

The main reason I believe that rice is one of the most commonly used fillers for DIY heating pads is because of its heat retention.

When heated, rice maintained detectable heat for about 25 minutes.


When the rice left the microwave, it was very hot and took at least 5-10 minutes to cool down to a comfortable temperature.

It only had about a 10 minute window of usable heat, before it cooled down too much to offer any benefit.


Durability was the main category in which rice failed with flying colors.

After being heated only two times, I noticed significant browning.

This is due to the fact that unlike many of the other food stuffs on this list, plain rice does not have a kernel, making it less dense and unable to retain heat without burning.

Another issue that I had with the rice right off the bat was that when I opened up a fairly new bag of rice, I could already see weevils.

No offense, I don't want any creepy crawlies anywhere near me when I'm not feeling good.


Rice contoured better than the corn, however it was still somewhat bulky.

It did provide weight, but not as much as I would have liked.

Availability and Cost

Bags of rice are found in every grocery store anywhere in the world and is one of the cheapest fillers that you can buy.

The bag of rice I bought was two pounds for $2.


After a couple of rounds of being heated, a smell of cooking rice could be detected as well as a hint of burning.

#9 Cherry Pits

white bowl of dried cherry pits

Cherry pits are cherry pits that have been cleaned and dried for crafting use.

Heat Retention

Cherry pits were a huge disappointment. 

When I read about them online, I was very excited to try them out, especially when I saw how some people described them smelling like cherry pie when they were heated.


That wasn't the case.

When they came out of the microwave, they were slightly too hot to touch and in under 10 minutes became cold.


Cherry pits are surprising fragile, being almost hallow in nature (they do make good filling for rattles).

From my experiments, they don't seem prone to rot or mold, but they do have the propensity to break.

When heated up, they didn't show any signs of burning.


Out of all of the different fillings, cherry pits performed the worst in terms of comfort.

The large round pits made the bag very lumpy, and the light density of the pits themselves offered almost zero pressure.

Availability and Cost

I searched for cherry pits and was able to find a small bag for them for sell on Amazon and Etsy.

The bag I purchased was around $13, which included shipping and handling.


I was very disappointed that once the cherry pits were heated they didn't smell like any cherry pie which I have ever eaten.

They did have a slight hint of natural cherry scent, but nothing that was overly noticeable.

#10 Clay Beads

white bowl of clay gardening beads

Clay beads are round lava stone pieces that are used in gardening, especially in regards to hydroponics.

Heat Retention

Of all the heating pad fillers, clay beads performed the worse when it came to heat retention, even when being heated twice the amount of time as the others.

Initially, I thought that clay beads would perform comparably to lava sand since both are made of minerals.

However, whether it be their light density or large surface area, the clay beads only retained detectable heat for 5 minutes.


One thing that clay beads has going for them in terms of being a heating pad filler is their durability.

Since they are made of clay, they do not rot, mold, or attract pests.

They can be heated up time and time again (because of their low heat retention, you'll have to), without burning.


Clay beads are very large, round, and light.

They do not contour very comfortably to a body's curves, and are very lumpy.

They also are very light, providing almost no extra weight for pressure.

Availability and Cost

According to online sources, clay beads can be generally purchased in gardening centers.

Apparently gardening centers that I didn't know about, because when I went to a variety of local garden centers no one had any, nor did they know where I could find them.

I then turned to Amazon and was able to purchase a small bag of them for $13,

If you would like to try them, make sure to use search terms including hydroponics to find them online.


To put it simply, no matter how hot they get they smell like dirt.

Best Heating Pad Filler Conclusion

After testing out the ten most common fillers, I noticed the following qualities that made for the best fillers:

  • Density
  • Color
  • Size of individual pieces
  • Resistance to perishability
  • Kernel

Although there are other fillers out there that are not included in this list, I believe the sampling of fillers has yielded a pattern in determining what makes a good heating pad filler.


The best heating pad filler is dense, making the area underneath the surface able to retain heat longer than less dense materials.


It is a given fact that darker colors retain more heat, this is also true when it comes to warming up fillers for heating pads.

The darker the color, the more heat the filling retains.

Size of Individual Pieces

From what I observed, it seemed the smaller the actual pieces of the filling, the longer it was able to retain heat.

Resistance to Perishability

The more perishable the material, the more likely it was to eventually burn.

Although the food stuff fillers performed well during the tests, there was a point when they couldn't be safely reheated.

Placing food stuff in the microwave and accidently overheating it was a problem that the non food stuff fillings didn't have to worry about.


When it came to food stuff heat pad fillings, the food stuffs with kernels proved to have the best heat retention and most resistance to burning.

Last Remarks

If you are looking for the best heating pad and heating pad filler, it's not about how cute or cheap a heating pad is, it's about the value it can offer you.

That is why I believe that lava sand came out as the overall winner in these tests.

When making or buying a heating pad keep in mind the importance of what is being repeatedly heated up inside of it. 

Choose the heat pad filler that can give you the comfort and relief that you are looking for.