I've been vaping for about four years now. For the first two years, I purchased store bought e-liquids. I had a frequent problem with my coils burning out. No matter how hard I tried, it seemed that I would burn coils on a regular basis (at least once or twice per week.) It got to the point that it was so annoying that I almost gave up and went back to smoking real cigs. But then I began buying DIY materials and mixing my own juice. Guess what? I rarely burn out coils anymore. Seriously, when I am vaping my own DIY juice, I only burn a coil about once per month. I've actually had coils last for over two months. Recently I was away from home and I ran out of juice, so I bought a bottle of premium liquid from a vape shop. Guess what? I burned my coil in less than an hour! I have no idea why this happens? Perhaps the store bought liquids are generally mixed too thick to quickly absorb into the cotton in the coils? I'm not sure, but it is definitely a real phenomenon for me. Has anyone else experienced this problem? It seems that vv/vw or temp control doesn't make a difference. Store bought juices burn my coils.