Just to offer another option, VapersTek.org is the smoothest, cleanes nic I've personally experienced. It is virtually invisible in mixes. While not the cheapest at $120 per liter of 100 mg/ml nic liquid. Incidentally, this size and strength will always yield the lowest cost per ml in your final mix. VT just lowered the price of their excellent VG and word on the grapevine is that the premium nic will soon get a price reduction as well. Many less-demanding vapors and those who mix primarily tobacco flavorings are thrilled (as I am) with the VT 'Throat Hit' nic product at the every day screaming deal of $25 per liter which product is actually better than the $40 to $50 'bargain brands' available elsewhere.
I understand that Carolina Xtract is a fine product but at those prices I will never find out myself. I don't know how much better it can be than undetectable. I have done business with a great guy so I won't name names but I don't buy from him any longer because he now sells a liter of 100 mg/ml for over $300. Great product. but $300 great? I'll never know. Those with an unlimited DIY budget (which term may be an oxymoron of sorts), please PM me for details.
"If you had the choice between World Peace and Bill Gate's fortune, what color would you Lamborghini be?"
- Will Ferrell