CO2 extraction, also less commonly known as supercritical fluid extraction, is solvent-free, mess-free, and very expensive. It’s also very popular with pros because the product is completely without toxins (unlike, as I’ve said, is the case with butane and propane), while retaining a terpenes-rich flavor.
https://www.thekindpen.com/14-different-kinds-of-weed-concentrates/