UltrAspire Formula 250


Basic summary: A small collapsible hybrid container with a high-flow valve opening that can be used for fluids, gels, and thicker content like applesauce or nut butters. The container has a capacity of 250ml and fits easily into a bottle holder when full, and into a small pocket when empty. The Formula 250 allows for transport of personalized nutrition needs on the go, with easy cleaning in the dishwasher or by hand when you’re finished.

MSRP: $13


  • Capacity: 250ml (8.5 oz)
  • Weight: 57g (0.125 lbs)
  • Dimensions: 3” x 2.25” x 7.5”
  • Material construction: seamless, stain resistant soft silicone
  • Odor- and taste-free material
  • Large mouth opening with flip top cap
  • Built in loop for hang drying

Deep dive:

Customization of nutrition isn’t just for elites anymore; more and more runners are taking care of their hydration and calorie needs individually at ultras instead of relying on what they might find at aid stations.

In that spirit comes the Formula 250, a versatile container that can be used for transport of fluids, concentrated powders, gels, or substances of thicker consistency. It allows you to prepare your race day nutritional needs in advance, and eliminates the problem of what to do with multiple wrappers or empty Ziploc bags that are discarded. When it’s full, it rests easily in the front vest pocket of most race vests, and when it’s empty it can be collapsed down to stow inside a zipper pocket.



Two key design elements that enable multi-purpose use are the use of soft, seamless silicone in the main compartment, which is pleasantly taste- and odor-free, and the high flow valve that is wide enough to allow thicker contents to pass through easily. The valve snaps open and shut in an easy and secure manner, and is fairly easy to operate with just your thumb, but if the contents of the flask are relatively thin, it’s best to hold the cap when flipping open the top, so the contents don’t pop out unexpectedly.


Although you can carry pure fluids in the Formula 250, the volume is quite low compared to standard water bottles, so it doesn’t really distinguish itself in comparison to other soft flask containers on the market. However, one interesting strategy we found was to use the flask to carry concentrated drink powder mixed with just a slight amount of water to help it flow through the valve more easily. Let’s say you’re wearing a traditional hydration bladder during an ultra, and you don’t like the drink mix being offered. With a flask full of your favorite powder in concentrated form, you can squirt a bit of it into your reservoir before filling the rest with water, so you can stick with the drink that works for you.

In a similar manner, the Formula 250 can hold straight gels squeezed from their packets, or gels mixed with a smaller volume of water. We were able to squeeze about 15-18 single serving gels in our flask, with the variability due to the packet size between brands. Raw gel can be squeezed out quickly even without being diluted with water, and the residual amount of gel left behind when completely squeezed out is noticeably less than other gel flasks we’ve used.


Because it’s a soft sided container, the Formula 250 doesn’t stand up on its own, so you need to place it inside a cup or mug when filling it. After use, it can be rinsed with soap and water, and the main container has a built-in drying hook on the bottom for easy hang drying. The seamless silicone is simple to rinse and clean by hand – pour soap and water in, close the flask, and shake a few times – but the hard plastic neck assembly is a little bit trickier as gels tend to get trapped in the interior screw mechanism ridges. When this happens, we put the cap through the dishwasher, and that blasts the residue out quite effectively.


UltrAspire’s Formula 250 is a deceptively simple-looking item that is actually rather innovative in its design and functionality. It provides a variety of options for customizing your race day nutrition so you can feel confident that you’ll have your preferred energy source all day long.


About Author

Donald is a physical therapist, California native, barefoot aficionado, and father of three with more than 25 years of experience in endurance sports. He was a collegiate rower at UCLA, then dabbled in marathons and Ironman-distance triathlons before falling in love with ultras in the early 2000s. His favorite locations to run include Marin County, CA, and the Sierra Nevada mountains, and he loves exploring America's National Parks. When he's not training for ultramarathons, he enjoys hiking or slacklining with his family in Monterey County, CA.

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