Issue with Soft Bath bombs

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New Member
Mar 8, 2022
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I have been doing bath bomb experiments for a couple of months now and about over a month ago got the right consistency (or so i thought) and therefore submitted my recipes for cosmetic safety assessment. Since then i have been doing batches however now for some reason bombs are now soft, if you press enough they just crumble to bits.. this is days after drying. I use the same recipe as before and previous bombs i had were made more towards beginning of the year which makes me think could the humidity be the issue, i live in UK (humidity between 70-90%.

My recipe is below. my problem is as i have already paid for the safety assessment quite a bit i was hoping not to add/remove too many ingredients. I noticed there is a user on etsy selling their bath bombs and their ingredients are close to mine, the only difference is they are using coconut oil as well with almond oil and witch hazel in each bomb and do not have any salt in them and their bombs are rock hard. I would be hoping to be close to that as I have already purchased bulk ingedients and wouldnt want them going to waste or make a loss.. I dont mind adding the coconut oil and leaving epsom salt out if need be, i could probably try to resell it. I guess my question is does anyone know whether it would be possible to get workable bath bombs with the ingredients rather than purchasing more different ingredients? any input is appreciated as i'm a bit at a loss here.

200g bicarb
100g citric acid
100g corn starch
100g epsom salt
9g almond oil
5g poly 80
7-10g essential oil depending which one
if 7g then adding witch hazel 3g , if 10g then leaving it out


Nov 21, 2013
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Too much corn starch and Epsom salt. You need to lower the percentage to 10%. It's very humid here. I use soda 60%,citric acid30%, 5%goat milk powder & 5% arrowroot. My bombs are hard and sturdy despite the humidity.


Staff member
Supporting Member
Oct 14, 2007
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I use melted cocoa butter in my bath bombs and they get very hard.

Mar 18, 2022
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Cream of tartar will help harden and keep bath bombs hard. Here is a great recipe. The witch hazel and dye is mixed into the baking soda and salt. Then the citric acid and cream of tartar mixed in. Then Poly 80, fragrance, and oil. The citric acid does not react with moisture when using this method. Humidity is ideal at 40%. I put newly made bombs in a room with dehumidifier. This recipe uses a press but I make same recipe using metal hand held spheres and it works perfectly. Sometimes I add Bioterge 90 powder to the mix. Winter Solstice Bath Bombs - Humblebee & Me