OMM
OMM Ultra Flexi Flask 350 mL Bite Valve
- Weight for its size: 8/10 How much it adds to your pack for the water it holds.
- Packed size (empty): 8/10 How much room it takes up when it is empty, for the water it holds.
Lowest price we found
£14.99 at Ultralight Outdoor Gear
Go to Ultralight Outdoor Gear Compare 2 shopsMountain marathons, fell running and fast days in the hills where 350 mL in a pocket is enough
- Type
- Soft
- Capacity
- 0.35 L
- Weight
- 37 g
- Packed
- Not published
Where to buy
Ultralight Outdoor Gear £14.99 In stock. Free UK delivery on orders over £15; under that, the shop shows the charge at checkout.
View at shop: Ultralight Outdoor GearOMM £15 In stock. Delivery £6. OMM's own shop. UK page lists 37 g and 0.35 L; OMM's German page for the same product lists 25 g. £6 Royal Mail Tracked 48 under £50. Cotswold Outdoor and Snow+Rock sell only a twin pack.
View at shop: OMMPrices checked 8 Nov 2026 on each shop's own page; shops can change them. We earn no commission on these links; shops are listed by price. More
Our ratings (out of 10)
1 to 10, compared with the whole market. Each says what it's based on. How we score
Weight for its size
From maker's figures 8/10How much it adds to your pack for the water it holds. 8: Clearly better than most.
OMM's UK page lists 37 g for 0.35 L: 106 g per litre, in the 100-179 g/L band. OMM's German page for the same product code (OG014) lists 25 g (71 g per litre, which would be the top band); where the maker's own pages differ we band the one that scores lower, so 37 g. OMM's page said 25 g up to January 2023 and 37 g from March 2024 (Internet Archive). Ultralight Outdoor Gear lists 24 g.
Packed size (empty)
Estimate from maker's specs: soft bottle: rolls up when empty 8/10How much room it takes up when it is empty, for the water it holds. 8: Clearly better than most.
Estimate from maker's specs
In short
Good for
- Mountain marathons, fell running and fast days in the hills where 350 mL in a pocket is enough
- A light spare flask, or one to carry gels and drink mix
- Hikers already using OMM packs with stash pockets
Strengths
- 37 g for 350 mL: 106 g per litre
- Compresses as you drink, so less sloshing (OMM)
- Wide opening for filling and cleaning
- Interchangeable bite valve and straw (OMM)
- TPU body, BPA, PVC and phthalate free (OMM)
Weaknesses
- OMM's UK page says 37 g but its German page says 25 g (we use the heavier, which scores lower), and Ultralight Outdoor Gear lists 24 g
- OMM gives no rolled-up size, so we cannot score packed size
- Sold singly by OMM and Ultralight Outdoor Gear only; Cotswold Outdoor and Snow+Rock sell a twin pack
- No independent test found, so ease of use and durability are estimates, not reviewed scores
Sources
We haven't tested this ourselves. Every score comes from these specs, tests and reviews.