Will bath bombs fizz in cold water?

Bath bombs are a great way to add some fun and relaxation to your bath, but it turns out that cold water doesn’t work for them. But how true is this?

Bath bombs will fizz in cold water, however at a much slower pace. This is due to cold water molecules moving around as they are in hotter temperatures. It is possible to make bath bombs fizz better in cold water by adding more citric acid, using less cornstarch, or excluding it from the recipe.

If you’re a bath bomb fanatic, you’d know that certain variables affect the success rates of a good bath bomb session. Although not guaranteed in every case, one big determinant for fizz or eruption (although not guaranteed in every case) is water temperature – so how does this work? Well, let’s find out, shall we?

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Does temperature affect bath bombs?

Yes. The water’s temperature affects how your bath bombs work and determines how quickly it will fizz. It’s also worth noting that bath bombs are meant to be used with warm water for a better fizzing effect, but they won’t work in cold water, this is especially the case if you decide to make your own homemade bath bombs.

The “fizz” that your bath bombs produce happens due to a chemical reaction, which comes from two of the main ingredients: sodium carbonate (a base) and citric acid. When you add water to the equation, these ingredients will react together and will start “fizzing.” We’ll go into the technical part later in the article.

It is recommended to use bath bombs with warm water because of the thermal energy that heat adds to it, making the water molecules move around relentlessly. This effect causes the components mentioned above to collide constantly, which makes the bath bomb fizz faster based on how hot the water is.

Experts say that the optimal temperature for your bath is between 104 and 112ºF, which is enough thermal energy for a regular bath bomb to start fizzing. However, if you experiment with the temperatures for a while, you’ll figure out the pace you’d like your bath bombs to fizz.

Will bath bombs fizz in cold water?

While bath bombs do fizz in cold water, they’ll do so very slowly. Since water is still present, the chemical reaction between sodium bicarbonate and citric acid still happens. However, the carbon dioxide gas produced as a result of the chemical reaction is barely noticeable, which is why the bubbles and eruptions are absent.

If you’re lucky, you may be able to see a slight “fizz” in cold water, but it will not be the same reaction you would obtain if you used cold water. Furthermore, some of the bath bomb’s components may end up accumulating on the surface.

If you use commercial bath bombs, you’re very unlikely to make it possible for you to make them fizz “faster” in cold water. However, if you make DIY bath bombs, you can adjust certain ingredients to make the bath bomb work hastily in cold water.

Will the bath bomb react faster in hot or cold water?

As evidenced above, bath bombs will react quicker to hot water. While they may still work in cold water, the chemical reaction may not be as noticeable as you’d like. This happens because, in cold water, the water molecules are not moving around as they are in hotter temperatures. Furthermore, the presence of cornstarch in the recipe makes it harder for the fizz reaction to happen, as this component is meant to slow down the effect. After a few moments, it can also make some of the ingredients clump on the surface.

Contrary to this, a bath bomb will react faster in hot water due to the high amount of thermal energy it contains. Heat makes the water molecules move around individually and collide with each other constantly, making it easier for the fizz effect to appear as the sodium bicarbonate and the citric acid will react quicker.

However, there are ways to make a bath bomb work better in cold water.

How to make a bath bomb that works in cold water

If you make DIY bath bombs frequently, then you’ll be happy to hear that you can modify the structure of your bath bombs to make them work in cold water as they would in hotter temperatures. Here we mention some of the ways you can take into account to make bath bombs that react faster in cold water.

  1. Use more citric acid.

Increasing the citric acid ratio to baking soda can work if you want to increase the fizz effect. There isn’t an exact way of making a bath bomb fizz perfectly in cold water, as each person has a different preference. However, you can experiment for a while until you find out the optimal recipe for your cold bath bombs.

  1. Use less cornstarch, or exclude it from the recipe.

Cornstarch is used in bath bombs to slow down the fizz reaction. Therefore, it plays an essential role in how your bath bombs react to hot or cold water. Since you’re making a cold-water bath bomb, you can use less cornstarch or exclude it from the process straightforwardly for better results.

What temperature will make a bath bomb fizz better?

According to experts, the optimal bath or shower water temperature is between 104 and 112ºF – which equals 40-44.4ºC. This temperature is hot enough for your bath bombs to fizz efficiently and for you to get in the bathwater safely. However, keep in mind that your bath bomb will react faster the hotter the water is.

Two studies, one from the UK and one from Japan, determined that keeping your bath water temperature within the temperature levels mentioned above can help you feel more relaxed. The UK study confirmed that keeping your water at 104ºF makes you spend the same energy you’d use in a 30-minute walk.

How does water temperature affect the fizz and eruption of bath bombs? 

In hot water, the water molecules are “bouncing” around and colliding with each other constantly. This is because thermal energy is present, which also means that higher temperatures equal more energy. You can easily notice this reaction when the water is boiling, as it creates bubbles, and the water moves around, too.

What does this reaction have to do with the fizz and eruption of bath bombs?

Well, it’s all about the acid-base reaction. In bath bombs, the fizz reaction is caused by the base (sodium bicarbonate) and the acid (citric acid). Keeping these ingredients together in a dry place won’t react because they require water molecules to trigger the fizz reaction.

In hot water, water molecules are in constant movement, making it easier for the base and the acid to react. The hotter the water, the quicker this reaction will be.

Now, we haven’t forgotten about the fizz and “eruption” reaction. The acid-base reaction also releases CO2 gas, which is responsible for all the bubbles and the fizz you notice when you drop the bath bomb in hot water.

It’s quite complicated for this reaction to happen this quickly if you use cold water because the water molecules are basically inert. When you drop a bath bomb in cold water, the acid-base reaction still happens, but the effect is barely noticeable for the human eye. 

If you’d like your bath bombs to work correctly, you can use more citric acid in your recipe, or you can remove the cornstarch from it. Both of these ingredients are directly related to the fizz and eruption of your bath bombs.


So, would the bath bombs you currently have work in cold water? Probably not, and neither would the commercial bath bombs. It is because they were made specifically to react with warm water. However, if you enjoy doing DIY projects, you can always make bath bombs that work in cold water.

It can take you a while to perfect your “cold bath bomb” recipe, but at least you will be able to take a few relaxing cool baths until you figure out the recipe that works best for you.

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