I had never used these soft flasks before, but in order to use Tailwind products during my Boston Marathon, I had to carry all of my own fuel. I had tried it on a training run & it worked, so I took it to Boson. A VERY not-welcome surprise when after stopping to add water to the HiCarb fuel in my bottle I shook it up and on my very first attempted sip, the drinking tip/spout popped off!! Lost some fluid, a bunch of adrenaline, and thankfully maybe only a few seconds. I can't even remember if I picked the tip up off the ground or if I caught it against my body. I HAD to find a way to use that fuel and was able to force the tip back onto the bottle (it wasn't the large opening that popped open), but ... YIKES! That was an unpleasant shock and not great for my mindset. I didn't have that problem again, but I also haven't used it again.