What are resin additives/customizers made of?

I have seen a few shops offering liquids/pastes which can be mixed into UV resin to make the final print softer or harder, or to make it cure faster or less viscous. Examples are the BlueTech customizers or the 3dresyns additives (can’t add links cause I’m new)

While the resins themselves have safety sheets which give the chemicals contained inside them, I was not able to find any details about these additives. Does anyone know what’s in them?