Can Heating Pads Catch On Fire?

Heating pads are a great source of heat and deep pressure stimulation therapy. However, many people are afraid of taking advantage of its soothing and healing properties.

Why?

Because many people are afraid that placing heating pads in a microwave will combust or catch on fire.

When heated correctly, it is perfectly safe to heat a heating pad in the microwave. Instances of heating pads catching on fire usually occur if the pad is heated too long, or the coverings are made from combustible materials.

In order to use a heating pad safely, there are a few steps to keep in mind when making/buying, heating, and using your heating pad.

Finger pressing microwave button

How To Safely Heat Up a Heating Pad In The Microwave

Heat packs are a great way to use heat therapy to aches ranging from menstrual cramps to arthritis.

However, you may have heard horror stories on how some heat packs caught on fire in a microwave.

Let me assure you, instances of heat packs catching fire are few and each time was because they were not heated properly.

If you follow the instructions that come with your heat pack, or you follow these simple rules, you can enjoy the relief your heat pack offers without worrying about calling the fire department.

Instructions on How to Heat Up Heat Packs

  1. Only use heat bags that are made from non-combustible materials.
  2. Do not purchase or make a bag that has metal on it (including zippers)
  3. Only heat the bag for the time listed on the instructions (Usually 3 minutes or under).
  4. Heat your heat pad in a clean microwave or on a plate.
  5. If your heating pad is filled with food items (i.e. rice, beans, corn, flax, etc.) place a small glass of water inside the microwave with the heat pad as you microwave it (1/2 a cup in a microwavable cup is advisable).
  6. After multiple uses, replace food stuffs fillings when you notice a slight burning scent. (Doesn't apply to Lavabags).

Printable Instructions For Rice Heat Packs, Bean Bags, Lavabags, and Other Heat Packs

Best Material For Heat Pads

When not overheated, fabrics made from natural materials such as cotton, linen and wool hold up well in the microwave.

However, materials made of synthetic substances such as nylon and fabric containing polyester are not recommended for making heat packs.

That is because these fabrics have a tendency to melt inside the microwave.

To avoid burning fabric made of cotton, linen, or wool, place a small microwavable cup of water when heating a heat pad inside the microwave.

Another method to avoid burning fabric is to slightly wet the material before heating it.

Never Put Metal in the Microwave

When making or buying a homemade heat pack, make sure never to put a metal zipper on it. 

That is because metal and microwaves do not work together.

Growing up, my parent's owned some plates that had metal rims on them.

Being young, sometimes I made the mistake of heating my microwavable chimichangas on them, only to witness sparks begin flying inside the microwave.

Needless to say, it's easy to panic when sparks fly inside of the microwave.

How Do Microwaves Work

Like the name suggests, microwave ovens create microwaves.

These microwaves bounce around in the oven until they become absorbed by the water molecules found in food.

The water molecules then oscillate (moving back and forth, in this case very very fast), causing the food to get warm.

Microwaves can pass through pretty much every substance, except for metal.

In fact, metal deflects the microwaves away, causing them to jump around even more erratically, damaging the inside of the microwave.

All of these bouncing microwaves can cause the metal of an object to heat up, and even create a electrical field around its edges resulting in sparks. 

Even the smallest amount of metal in a microwave can damage it (MIT School of Engineering).

How Long Do You Heat Up a Heat Pad?

Because anything you put in a microwave for too long can burn or even combust, it is important not to overheat your heat pack.

Heat pad heating times are determined by the wattage of the microwave, the materials that make up the heat pad, and the density of the heat pad.

Generally speaking, most heat pads should not be heated for more than three minutes, with heat times between 1 to 2 minutes being the average.

If you buy a heat pad, make sure you follow the directions that come with the product.

For homemade heat packs, keep to the 1 to 2 minute average.

Determining Microwave Wattage

If you do not know the wattage of your microwave, look up your brand and model type online.

Most microwaves are usually between 600-1200 watts.

If you are unable to find the information online, you can figure out wattage by how long it takes to boil a cup of water.

If a cup of water takes 1 1/2 minutes to boil, then you 1200 watt microwave.

The longer it takes to heat a cup of water, the lower the microwave wattage.

Time To Heat 1 Cup Water  Microwave Wattage
1 1/2 minutes 1,200
2 minutes 1,000
1 1/2 minutes 800
3 minutes 700
4 minutes 600

(Information found on Epicurious)

Heating a Heat Pad in a Clean Microwave

When heating a heat pad in a microwave, it is important that the microwave is reasonably clean.

Not only does heating a heat pad in a clean microwave keep the pad itself clean, but it reduces the chances of crumbs and leftover bits and pieces of food from catching on fire if microwaved too long.

Add Water When Heating Heat Pads

We discussed the role that water molecules play when heating up heat pads in the microwave.

To help maintain a certain amount of moisture in the microwave, it is generally recommended that a small cup of water be placed in the microwave along with the heat pad.

This will add enough moisture so that the fabric and contents of the heat pad do not burn as easily.

Make sure the glass containing the water is microwavable safe.

Woman setting timer on microwave

Does Heat Pad Filling Need to Be Replaced?

Heat pads that are filled with food items such as wheat, rice, corn, flax, and other materials do need to be replaced on occasion.

Food stuffs do not last forever, although some last longer than other.

Eventually, they will rot or go rancid, and burn after repeated heating.

They also trap mold and bacteria and are not easily cleaned.

Foodstuff filled heating pads also will eventually smell, either from the rot or from burning.

If you choose to have a heat pad with perishable filling, consider having a heat pad that is easy to open and remove contents, such as a knotted sock.

Change foodstuff fillings out if you begin to notice strange odors arising from them.

However, there is better heat pad filling option that never rots or smells and can last without needing to be replaced.

What filling is that?

Lava Sand Heat Packs

Lava sand filled heat packs are wonderful because the filling, lava sand never smells or burns.

Although, due to their covers it is important not to overheat them, the lava sand itself never ignites.

This makes for a safe, long lasting pack that is  perfect for alleviating various aches and pains.

Lava packs last for years, and if the covering needs to be replaced, the lava sand itself can be saved and placed in a new pack.

Frequently Asked Questions

How Long do Heating Pads Last?

Depending on their contents, heating pads can last for months or even years. 

Heating pads, such as Lava Bags have contents that last indefinitely, although the covers may need occasional replacement.

There is no set time on how long a heating pad lasts.

Heating pads containing rice, wheat, corn, and other food substances can last a few months to a few years, depending on exposure to moisture, size of individual filling pieces, and number of uses.

In general, the larger the grain or kernel, the longer lasting the heat pack.

Small grained heat packs, such as flax or wheat begin to burn easier than larger kernelled bags made of corn or cherry pits.

If a pad is exposed to too much moisture, rot and decay begin to set in and the contents and even the cover will have to be replaced.

When a pack begins to smell like rot, or has signs of burning, the pack needs to be replaced.

What Happens if you Overheat a Wheat Bag?

Since wheat berries and kernels are small, it is very easy for them to overheat.

The main sign that a wheat pack/bag is being overheated is a distinct burning smell.

Wheat that is overheated in a heat pad begins to burn.

If it keeps getting overheated, the wheat will continue to burn, increasing the chances of it catching on fire.

Yes, it is possible for wheat bags/packs to catch fire in the microwave if the filler is too dry, not enough water is present, and it is microwaved longer than the recommended time.

It is a good idea to check the contents of a food stuff heat pad each time before use to make sure that the wheat or other material isn't burnt or needs to be replaced.

As mentioned earlier, to help prevent burning, place a small glass of water in the microwave along with the heat pad to provide adequate moisture.

What Should I Do if My Heat Pack Catches On Fire?

If a heat pad or anything else catches on fire in a microwave, turn off the microwave immediately, and if possible unplug it.

Do Not Open The Microwave

Wait until the fire suffocates itself out before you open the microwave door.

Can You Put A Sock In A Microwave?

As long as the sock itself is made of natural fibers, and isn't made from polyester or other combustible materials, it is safe to put a sock in the microwave as long as :

  • It isn't heated too long
  • There is moisture present in the microwave
  • Any materials filling the sock are not combustible or overly cooked.

It isn't recommended placing clothing in a microwave, however socks are a fast and easy way to create a heat pad as long as it is heated correctly.