Sin City Vapor Salt Nic
There's a difference between "freebase" nicotine, and the newer "nic salts".
Freebase nicotine is the purest form of nicotine and is the default "go-to" for most manufacturers. This solution of nicotine is simply added to a mixture of vegetable glycerin (VG) and propylene glycol (PG) which "carry" the nicotine with them when vaped. It's also what is used in nicotine replacement therapies—like gums, patches, sprays, and lozenges.