Bath bombs, a fun DIY activity with kids

Our kids love to take a bath. And they love it even more when a bath bomb is involved. If you don’t know what bath bombs are, they’re these balls made of baking soda and citric acid, that dissolve in a bubbly way in your bath. The kids love them, mostly because the ones we get them have a tiny plastic toy hidden inside them.

Bath bombs with toys inside are easy to find in Japan for 108 yen (about 1 USD) in one of the many 100 yen shops. And the kids love them. So, even though they’re not the “$6 a pop” kind of bath bombs you can find at Lush, I was getting worried as the kids started to ask to take a bath more and more often, and the obvious reason was that they expected the bath to involve a bath bomb.

It was high time to see if we could make our own, and how much that would actually cost. A good way to have a fun DIY activity with the kids, and to flex the frugal muscle.

I won’t go into the recipe of the bath bombs, it’s very easy to find online (for those who care, I believe this is the recipe we used, although we used less water due to the humid weather), and involves baking soda, citric acid, and then some fancy stuff if you want to (in our case, we also added corn starch, epsom salts, essential oils, food colorants, and plastic toys).

All the required ingredients are ready

However I want to discuss the process of making them with the kids, and of course the cost.

Making our own bath bombs with the kids was very fun. There was a bit of stress involved as it was the first time we were making them, and Tokyo is extremely humid in the summer, which is the worst thing to have when trying to make bath bombs: an excess of humidity could trigger the reaction between the baking Soda and the citric acid, which would ruin the whole thing. So I was a bit nervous at the amount of liquid we were pouring into the whole thing, while the kids really wanted to get going and create the bath bombs. I’ll give more details on humidity below.

Once we got the basic mix ready (basically all the dry ingredients), choosing the essential oils and colors to add to the mix was probably a huge part of the fun. The kids decided to have some purple, yellow, and green bath bombs. We associated those with Lavender, Orange, and Tea essential oils respectively. Tiny drops of colorants and essential oil were more than enough. We split the dry mix into 3 parts, dropped the 3 colorant+oil mixes in there, mixed a bit more, adding just a tiny bit of water, and we were ready to craft the bath bombs.

Everything went so fast and was a bit chaotic (it’s pretty much like cooking, kind of tough to make it fun AND successful with young kids who all want to be heavily involved in the process, especially when it’s your first time with a given recipe). The result is that I forgot to take pictures during most of the event. I just have before/after kind of pictures.

The dry ingredients are mixed. After that I forgot to take pictures of the process

The bath bombs are shaped and ready to dry

The Toys

Our 6 year old son told us that if he saw the toys ahead of time, the bath bombs would not be fun. A big part of the fun is discovering what toy is hidden inside the bath bomb as it dissolves in the water. So I ordered some cheap plastic toys online, and as we were making the bath bombs, my wife and I sneakily inserted a plastic toy in the center of the mold before pressing the molds together. That worked out ok, and the kids did not have their surprise ruined ๐Ÿ™‚

The kind of rubber toys we got for cheap on aliexpress. Perfect size, and safe in water.

Bath Bomb beginner mistakes, and dealing with high humidity

Making the mix and crafting the bath bombs is surprisingly fast, and at first we thought we had nailed it. The mix for bath bombs cannot be too humid (or the chemical reaction would start instantly), but it cannot be too dry either (or the bombs won’t be able to retain their shape and/or might crack during the drying process). We had something that worked ok. However, the complex part is drying the bath bombs, a process that can take up to 24h.

So, although initially we had great looking bath bombs, as we put them to dry, things didn’t go as planned.

Tokyo is very humid in Summer. We had about 80% humidity in the room when we were crafting the bath bombs. According to bath bomb experts, this is a recipe for disaster, as the bath bombs will not dry properly. I was aware of that and had a genius plan: bathrooms in Tokyo can be used to dry the laundry, as they have a special “heater/dryer” mode. And they’re well sealed. So, instead of putting our bath bombs to dry in a low temperature oven (which is recommended in humid areas), we instead put them in the bathroom, and set the vent to “drying”.

It kind of worked, but also kind of not. We were not too sure how to proceed, so we kept the bath bombs in one half of their molds.

Sadly, as the experts predicted, some of the bath bombs started expanding outside of their molds. Others dried a lot for the half that was outside of its mold, but not for the part that was inside. Others started to crack in the middle as they expanded, right where we had put the toy.

For a few hours, we had to battle with the bath bombs, mostly by trying to re-compress them regularly within their molds (while they were not fully dry), to force them to go back to the ideal spherical shape, and in a lame attempt at stopping the chemical reaction for some of them.

On the next day, things had turned out ok. Our bath bombs did not all have a “professional” look (although some of them did), but none of them had cracked (the toy surprise effect was preserved, and the bath bombs still looked spherical enough, except for one that looked maybe more like a cute mushroom), and overall they looked great from our kids’ perspective, and to us as first timers in this DIY experiment.

Another challenge was awaiting: getting the bath bombs out of their molds. As the bath bombs had expanded during the drying process, they were all very tightly stuck into their molds. I feared that I’d have to break them in order to get them out, which would have been a shame given how hard we’d tried to keep them spherical.

Ultimately, tapping the molds with a spoon allowed us to get the bath bombs out of their molds. and they were rock solid, so none of them broke in the process. I however damaged the shape of some of the molds by tapping them with the spoon ๐Ÿ™

We’ve learned a few lessons during this process, and we’ll try to change some of the methods next time we do bath bombs, specifically:

  • In humid weather, it is difficult to not get the bath bombs to expand during the drying process. If we try to dry them with excessive heat, they can crack. If we just use “natural” air flow, it is too humid and they will start expanding. In our case, they did both. I don’t have a good solution for that except 1) trying to put even less water in the mix initially or 2) avoid doing those in the summer when it is so insanely humid. The “dry” mode of our bathroom probably helped though and we would recommend it for other folks living in Tokyo who are trying to make bath bombs.
  • There is a proper way to mold the bath bombs. It is not to pack as much mix as possible in the two molds before compressing them, but instead to put excess of mix in both, without packing, and then press the two molds together. doing so will reduce the risk of cracks in the middle. Great video on the topic here.
  • Toys in the middle of the bath bomb make it even more difficult to avoid cracks, because they’re this “non sticking” piece preventing the two halves of the bath bomb from correctly merging together. We hope the technique above will help reduce the problems.
  • Keeping the bath bombs inside their molds until they’re done drying is probably a bad idea. Although it helps them keeping the right shape, it is also extremely difficult to get out once dry. Next time we’ll try to remove the molds after a few minutes, like we’ve seen on a few videos

The Cost

alright, so how costly was it to make our bath bombs? Let’s run the math a little bit. Here’s what I bought, from Amazon and Aliexpress:

  • food colorants Y355
  • Epsom salts 2.2kg Y1296
  • Citric Acid 2Kg Y1500
  • Baking Soda 2Kg Y686
  • Cornstach 1Kg Y893
  • Essential oil beginner’s set Y1000
  • 42 plastic toys $10.70 (price in dollars as I got those from Aliexpress and paid with my US card)

I will not count the price of the molds here because they are reusable, but in total I spent $11.34 on molds. This gave me 3 aluminum molds + 30 plastic molds. On Aliexpress again. You can practically use any kind of mold you have lying around, such as plastic Easter eggs or other things you might have lying around. Some people shape them in their existing muffin or donut baking molds.

It is difficult to estimate how much of food colorants and essential oils we used, but I’d say there is largely enough for 100 bath bombs in there, so I’ll divide the cost by 100 to estimate the individual cost. For the rest, in our first experiment, we’ve used approximately:

  • 180g baking soda (about 62 Yen)
  • 90g Epsom salts (about 53 yen)
  • 90g citric acid ( about 68 yen)
  • 70g corn starch ( about 63 yen)

That’s a total of 246 yen, which allowed us to make 8 bath bombs. Or 31 Yen per bath bomb.

Additionally, we spent

  • 1 toy per bath bomb ($0.26 per toy, that’s about 28 yen at the current rate.)
  • about 4 yen worth of food colorant
  • about 10 yen worth of essential oil

Result: 31 Yen for basic recipe + 28 yen for toy + 4 yen for colorant + 10 yen for essential oil = 73 yen per bath bomb (about 65 cents).

Hey, that’s a good 30% cheaper than the price of the cheap ones we can find in stores here. And they’re higher quality too, as the ones we can buy for kids in Japan don’t include epsom salts or essential oils as far as I can tell.

Obviously, we could reduce the costs here by not including the bath salts or the essential oils. Also worth mentioning that we’re not comparing apples to apples, as we created bath bombs that were significantly bigger than what is sold in 100 yen shops. Then again, almost half of the cost of our bath bombs is in the toy, and there’s not much we can do to reduce that part of the cost, but realistically by reducing the size of the bath bombs and removing the essential oils, we could reduce the cost to 50 yen per bath bomb (less than 50 cents). For grown ups who don’t care about the toys, the price would most likelyย  go down even further.

There’s obviously a problem that I’m not addressing here, which is that I bought all of that in bulk. And frankly, we won’t use these products massively for anything else than bath bombs (except maybe the baking soda). Our total cost is about 7000 yen ($63), meaning we’ll have to create more than 60 bath bombs in total for it to be “worth” it compared to the commercial option (and yeah, I’d need to buy more toys then…). But honestly, given how fun it was to make (and how much value can we give to an hour of a fun activity with the whole family? Most people pay more than what we spent here), and how much the kids enjoy having those in the bath, I can easily see how we will be making more than 60 bath bombs in the next few months. I also have hopes that ultimately we’ll become good enough at making them that we can start giving them away as presents to friends.

The options are infinite!

The final products, wrapped in individual bags to try and preserve them from humidity. Those are the ones our kids chose when it was time for bath. Also this picture confirms I’m not ready for pinterest yet ๐Ÿ™‚ Notice how one of them is multicolored. It was super easy to achieve by just packing some of the mix from the 3 different batches. By the way, yes, two kids = two bath bombs…

We’ve only done some basic bath bombs so far, but I’m excited at the many options. There are lots of variations one can think of to make those fun for the kids, or nice presents for friends. Variations of shapes (hearts instead of spheres, etc…), colors (I’ve seen people hiding a very concentrated colorant inside an otherwise white bath bomb. The surprise is to try and guess which color the bath will end up becoming. I’ve also seen reciped where only the bath salts were colored, etc…), perfumes (we have a “beginner’s kit” of essential oils that we’ll use for a while, but clearly my kids and I prefer the more “fruity” smells while my wife like something that smells more like perfume), etc…

One Response
  1. Mr. Tako

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