As noted already TNE is the oil based. Most people are now adding guaiacol/PS80/BA/BB to their water based and oil based.
Guaiacol is what many companies selling fina kits would list as a super solvent. It helps hold items that typically crash easily, it also decreases the pain. PS80 is added as a surfactant.
Guaiacol is very distinct in smell and if too much is added, it's really horrible and you will smell it in your sweat. Typically I do 75-100mg/ml, no pip and the water based will hold as a milky white substance, it still needs to be shaken prior to use but it doesn't completely separate like some of the old stuff. I had tne and suspension that was about a 20 out of 10 on the pain scale. Fuk it hurt and would leave the site swollen.
Honestly, even though I have access daily to free suspension that is completely painless, I don't use it. I don't see a point for myself. I hear so many guys say they get such a great boost while training and massive pumps, but supposedly are only using it pre wo, but I've never noticed much at all. Basically to me it's no different than using any other t except for frequency but I always run a base of c or e withit like most do. I'm not saying its not good and that I don't make gains but I have a hard time saying that exactly XYZ happens when I add it as a pre workout dose. I'm sure it can't hurt to have your system flooded with T during that time but isn't it something like 98% that is bound to albium and shbg anyway? I add proviron or mast prop to attempt to free up more but then again I can take dbol or whatever pre workout and never get any increased benefit that would be different from running a cycle like normal.
Sorry for the rant, I just think sometimes it gets hyped up and guys expect to much or have some placebo effect from hearing about it all the time, or maybe I just suck and am unlucky and don't get that good boost.