Hellfoam is when you mix fire chems and foam, making a extremely dangerous foam that will burn anyone inside of it. The foam will crit in a few seconds and is pretty much unescapable if you get caught in it.
A very simple hellfoam mix would be something like this:
50 units phlogiston
50 units fluorosurfactant
60 units chlorine trifluoride
20 units water
20 units napalm
While this isn’t the best possible mix, it’s still very efficient and eliminating anyone that you need to, but be aware, the mix is very hot and will melt trough hull plating leaving breaches, so grab EVA gear before you use one of these!