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How to Make Bath Bombs Harder | DIY Guide with Pro Tips!

How to Make Bath Bombs Harder
Written by Elizabeth Fincher
Last Update: August 10, 2023

The use of a bath bomb in the tub is a guilty pleasure. The fizzing makes your skin tingle. The fragrance in the hot bath water helps relieve stress.

But nothing is worse than a soft, fizzless bath bomb!

Let’s look at how to make a bath bomb harder.

Is Your Bath Bomb Too Soft?

The mixture is too wet

  • Your mixture may be too moist
  • Add more dry ingredients a little at a time till the mixture is just right
  • It is fizzy when you put it in the mold
  • There is no fizz when you drop it into the water

The mixture is too dry

  • Your bath bomb is crumbly
  • Removing it from the mold causes it to crumble

How to Make Bath Bombs Harder?

  • Put in less liquid when making the bath bomb
  • Use the least amount of water that makes the bomb hold its shape when you squeeze it in your hand
  • You may need to add baking soda and citric acid at a 2:1 ratio to equal out the moisture.
  • Use witch hazel instead of water
  • Use water-free fragrances and colors
  • 91% Isopropyl Alcohol is a better substitute for water and witch hazel
  • Include tapioca starch, cream of tartar, or kaolin clay in your mixture to get more fizz
  • Use coconut oil or cocoa butter to add moisture to the bath bomb and make it harder
  • Cornstarch can also be used to harden the bomb, but don’t use too much as it can stop the bath bomb from fizzling.

Time needed for bath bombs to harden

Although it depends on the recipe you use, but generally bath bombs take 4 – 12 hours to harden. For some mixtures you may need to wait 24 – 48 hours to make them hard enough. Leaving them overnight is enough in most cases.

If you want to reduce the waiting time, you can use oven, dehumidifier, or hairdryer to dry your bomb. The method will depend on how fast you want your bath bomb to harden.

Important Reminders

1. Containers must be airtight

Once your bath bombs are dried, they need to be stored in a cool, dry place in an air-tight container.

2. Store in low humidity

Humidity will make your bath bombs soft. Store them in a cool, dry place.

3. The secret to a dry bath bomb: Blow dryer

Using the blow dryer on your bath bombs for no more than 1 minute at a six inches from the bomb will dry the extra moisture without cracking your bomb.

4. Using a rubber band when wrapping

Once your bath bomb is in the mold, use rubber bands around the mold to keep the mold together and air-tight while it dries.

5. Silica gel: The secret to keeping a bath bomb dry!

Silica packs (found in almost everything you buy) can be saved in a Ziploc bag and used in the air-tight container you place your bath bombs in for extra moisture removal.

6. Dehumidifying the bath bomb

Living in a climate with high humidity or in the summer, using a dehumidifier if you have one will keep your bath bombs moisture-free until you use them.

7. Using cream of tartar

Adding Cream of Tartar and Kaolin Clay will make your bath bombs harder.  Cream of Tartar will react with the Citric Acid in your bath bombs, creating the best fizz when dropped into the bath.

8. Using cocoa butter

Cocoa butter is an excellent moisturizer. Adding Cocoa Butter to your bath bombs will add moisture to the bomb and help form a better bomb. The bomb will dry harder.

When dropped into the water, your skin will feel silkier.

9. Using coconut oil

Adding Coconut oil to your bath bombs not only moisturizes your skin but will also counter the drying effects of hot bathwater.

10. Using kaolin clay

Kaolin clay is used alone in your bath bombs or combined with Cream of Tartar.

Using it alone or with the Cream of Tartar will create a harder bath bomb.

11. The Snowball Test: Making the perfect bomb

To ensure your bath bomb is the correct consistency, you can do the snowball test. Take your bomb mixture and make a snowball; it is the perfect bath bomb if the ball holds its shape!

12. Don’t let that bomb expire

Even bath bombs have an expiration date. When stored in the perfect container, they need to be used in six months. After six months, they may no longer have a fragrance or fizz in the bathwater.

Tips for a Solid Bath Bomb

1. Dead sea salts are a bad idea

Never add Dead Sea Salts to a bath bomb; it will pull the moisture out of it and cause it to crumble.

2. Keep the oil percentage low

When adding coconut, sunflower, or avocado oil to a bath bomb, use a small amount. The ideal amount is 0.5 ounces per pound.

Too much oil can make the bomb slimy or fizzy, and it won’t hold its shape or dry correctly.

3. How much alcohol is enough?

Using 91% Isopropyl Alcohol as a liquid ingredient is the best way to add the Alcohol for moisture in the bath bomb.

The alcohol dissipates during the drying process, leaving the bath bomb hard. Add it with your wet ingredients.

Be careful to add small amounts until you find the exact amount that works for your bath bomb recipe.

4. Never use food coloring

Food coloring leaves color residue on your tub and skin. Use a powder or liquid colorant made to use in bath bombs.

It will create a non-toxic color for the bath bomb and will not add moisture that can change how the bath bomb dries.

Fizzing Out the Bath Bomb

The harder the bath bomb, the longer it fizzes in the bathwater. The right amount of color, fragrance, oils, and hardeners is the key to the perfect bath bomb.

Use the suggestions above so you will no longer have to ask, “Is my bath Bomb hard enough?”

Benefits of a Bath Bomb

1. Smells wonderful

A fragrant bath bomb turns your tub into a spa and relaxes you.

2. Keeps your skin moist

The oils used in a bath bomb help keep the moisture in your skin, making it feel silky.

3. Distresses your body and mind

The essential oils help you relax, while the fizzing rejuvenates your skin.

4. Helps detoxify your skin

The warmth of the water and the fizzing of the bomb detoxifies your skin.

5. Comes with healing properties

Essential oils can have anti-inflammatory, mood-lifting, and pain-decreasing properties.


1. Can I use too much colorant in a bath bomb?

Ans. Yes! Too much colorant can leave a colored ring around your tub! 1/8 teaspoon is a good starting amount.

To get a bit more color, add a bit more. If you use mica, do not use more than two teaspoons per pound. Adding Polysorbate 80 will help your colorant distribute more evenly.

Make sure to mix the colorant in until the color is even through the bath bomb mixture.

2. How much fragrance is too much?

Ans. You don’t want your bath bomb to smell so strong that you don’t want to use it!

The company that makes the fragrance you use in your bath bomb should have a chart that shows how much fragrance to use per pound.

If they don’t, you can go to Bramble Berry and use their Fragrance calculator.

They also have a video that will show you how to use the fragrance.

3. Why is the surface of my bath bomb looking so lumpy?

Ans.  Not sifting your dry ingredients and mixing until smooth will cause a bath bomb to appear lumpy.

Baking soda tends to clump, so be sure to sift it into the bomb mixture. If the fizzy ingredient has too much moisture, it may appear lumpy on the surface.

Make sure to mix the wet and dry ingredients really well to avoid this.

About the author

Elizabeth Fincher

Elizabeth started her career as an interior design artist at a multinational interior design farm. She completed her masters degree from the University of North Texas back in 2010. She was also a Spelling Bee runner-up when she was 14. She took interest in bathroom interior designing after joining her first job. Later she started her own firm as an independent artist. She’s been one of the founding members of Toiletsguide. She examines the design and ergonomics of the units we review and directs the interior decoration team of our in-house research facility. Elizabeth plays piano masterfully and always finds time to entertain us in between our busy schedules.

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