There are trail runs that are long enough that hydration is a beneficial effort, but short enough that I don't want to carry a full size water bottle. This is perfect, and it conforms to the small belt I wear. So lighter, more unrestricted, and 4 good swigs of water. I have not tried it with gels (primary design), but I'm sure it would work well. Twist cap is easy to use and seals tight... no leaks.