The design of traditional hip flasks contain both good and lousy UX. The good is that they're slightly curved, allowing them to nestle against your body when placed in a pocket. The bad is that they're made of metal and opaque, making it difficult to fill them to the top without spilling.
Better UX is offered in the flasks designed by Ragproper, a Utah-based company that makes them out of glass ("break resistant," they say, though they don't get more specific than that). They're made in both single (100mL) and double (240mL) sizes and are wrapped in leather or silicone, your choice They also come with a silicone funnel for easy filling.
The leather ones come in three traditional shades, as well as a light grey.
For those of you not as concerned with being discrete, the silicone offerings can be had in bolder colors.
One caveat about the leather models—the leather is permanently bonded to the flask. "We wanted to make sure [the flask] was sleek and easy to slide in and out of pockets," the company explains, "so the leather cover is not removable." I'd think that would make it impossible not to get the leather wet while rinsing the flask out. If that's a concern, you'll want to go with the silicone-sleeved ones, which are removable from the glass.
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