Review on FITLY Soft Flask - 12 Oz (350 Ml) - Shrink As You Drink Soft Water Bottle For Hydration Pack - Folding Water Bottle Ideal For Running, Hiking, Cycling, Climbing & Rigorous Activity (FLASK350) by Prentice Fossett

This is a good size. the silicone bottle and drink tip are good quality. I've only taken it out once, but I filled it with water and froze it, then put it in the side pocket of the spandex shorts, good for about an hour, keeping me a little cooler, and giving me enough to sip on for the longer (1.5 hr) run. The bite tip is also really good, and doesn't leak. I think the size might also be good to put a second one in my running bra.