When getting started making bath bombs, we were trying to decide the best bath bomb mold material. What we found out is there are really 4 types of molds: silicone, plastic, stainless steel, and aluminum. We bought sets of all materials, tried them out, and now only use 2 of them. We will discuss the 4 materials and which one we believe is actually the best bath bomb mold material.
The first one we tried was plastic. We bought 2 different sizes: 1.75″ and 2.75″. If you pack each one of these molds full, you bath bomb weight will be about 2 oz and 4.5 oz respectively. The one thing we found out is the plastic molds are very durable. They can be used over and over again. Eventually, they will crack and need to be replaced. But with the affordability of these Plastic Bath Bomb Molds, replacing them will not be an issue.
The next one was the silicone mold. This is a mold like the ones used for cakes, candies, etc. The one issue with this is you can not really pack the bath bomb material into the mold. Since it is made out of silicone, the sides will begin to bulge out. Plus, you need to leave the bath bombs in the molds overnight, which means you need a bunch of molds if you are making a bunch of bath bombs.
Third, we tried the Stainless Steel Bath Bomb Molds. These are the most expensive, but they are virtually indestructible. Very easy to use, has a nice smooth surface so the bath bomb slides right out. You can get a lot of compaction since there is no need in breaking of bending the mold. The only downside to these is the cost. But, once you buy them, you never need to buy them again.
Last, since we liked the stainless steel so much, we bought aluminum ones in the same size. They were much cheaper, so we decided to give them a try. These were terrible. For starters, the aluminum bath bomb mold is not smooth like the stainless steel. This led to bath bombs getting stuck and not having smooth surfaces. Another downside is when we dropped one, it dented. And there is no way to get the dent back out. So, while they were cheaper, they were our least favorite.
I the order of preference, we like the plastic ones and the stainless steel ones. I would not try the silicone or the aluminum bath bomb molds. You will be wasting your time and money. Stick with the stainless steel and the plastic ones and those will be the best bath bomb mold materials you can find.