https://vaporreporter.wordpress.com/2015/08/03/resistance-wire-safety-guide/ Stainless Steel 304/316 series. Safety rating- 95 (A+). SS has been used in medical procedures for years, though only recently has found its way into vaping coils. This is also the type of steel used in cookware. Why? Because it has a very high melting point (2400-2750 degrees F), and the questionable alloys in the steel (nickel being the biggest of concern) also require a high amount of heat (2200-2300 degrees F) before they begin to leach. I don’t know any mainstream vaping device that can reach those levels. Stainless Steel also brings a few added bonuses to the table. 304, 316, and 317 (welding wire, also known as GPlat in the community) contains enough nickel so where it can be used in a temperature controlled device. The only downside is it can be a bit tough to work with as it’s a little stiffer than any of the other metals on this list save titanium. Kanthal (Iron-Chromium-Aluminum)- 88 (B+). Kanthal was the second material used for resistance wire by vapers with good reason. Not only was it tougher than nichrome, but for those who were sensitive to nickel this was a perfect alternative. The safety concerns are two fold. Aluminum has it’s own stigma around it, but the big issue is the chrome content. With enough heat it can be transformed into it’s hexavalent (+6) oxide state, which is a known carcinogen, and leach. This would require you heating the coil to a orange hot state for an extended period of time. It’s why you should still replace your coils at some point, not just the wicking material. My rule is after every 3rd wick replacement and dry burn to remove the gunk. I have seen it suggested from others that you should anywhere between every time you change wicks to every 6th time. Kanthal isn’t compatible with temperature control devices as of writing this. Titanium- 72 (C). The first alternative to nickel for temperature control to hit the ecig scene. Ti has the highest melting point of all the materials we use (3040 degrees F), has been used in medical procedures, and is one of the toughest metals known to man. So why the average rating? Titanium Oxide, the byproduct of heating it up. The EPA and OSHA have put a limit on how much any worker can inhale during a day. This makes it a questionable material to use for vaping. As long as you aren’t dry burning it, or running it too hot you should be fine, but there is no long term vape testing to say one way or the other. It’s up to the user on whether or not they want to take that risk. Keep in mind this is the stiffest material to use for making coils, which depending on your build style can be a good or bad thing. NiChrome (Nickle-Chromium w/ some trace elements possible like iron)- 65 (D). Not only was it the first material vapers used for resistance wire, was the first documented material used for creating heat through electrical resistance back in 1905. It gets a very low grade on safety because it combines two metals with known issues. Nickel is a known carcinogen with other issues (will get to it), and as mentioned early Chromium Hexavalent is as well. It has a high melting point (2550 degrees F), but it doesn't do it a lot of good in real world applications because of how soft the alloy is. 32g nichrome will “pop” easier than 32g kanthal, SS, or Ti. That’s not to say it doesn't have its uses. For low wattage/temperature vaping you shouldn’t have any real issues. It has a lower resistance than the 3 mentioned before it, making it good for a heat sink material on some more exotic coil builds (think Clapton). It is also very flexible. For high wattage vapers or those sensitive to nickel can not suggest using it though. Nickel- 55 (F). This material gets a failing grade for a large number of reasons. 1- It’s a known carcinogen linked more often than not to lung cancer. 2- There are people with nickel allergies who simply can not use this material to begin with. While it to has a high melting point (2647 degrees F), it’s such a soft metal that it not only easily pops but is very hard to work with. Like NiChrome it does have a use though- As non-resistant wire (a cheaper alternative to silver or gold). It has the lowest resistance of all the materials listed, so it’s the perfect choice to have electricity run through without heating it up. That’s why it was used back in the day on GG Ithaka and the like as lead wires, and today is used on the SS coil heads by Aspire. Because no heat is generated by the energy flowing through it, there’s almost no chance of it leaching through, meaning there’s very little chance of you breathing any of it in.