Since running UTMB in 2018 I have fallen in love with the R-Go bottles. It was 12 F over night and only the squeeze tips froze. It was very easy to bite the ice and drink unrestricted. Also I carry my poles across the front. With my old soft flasks my piles would rub against my chest when they were empty. In the summer the hard bottles are easy to fill with ice to keep cool. I can’t say enough about how much I love these bottles. Oh yeah and they come in 800 ml too for those long stretches between watering holes.