Osprey
Osprey Hydraulics 500 mL Soft Flask
- Weight for its size: 9/10 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
£22.99 at Ultralight Outdoor Gear
Go to Ultralight Outdoor Gear Compare 2 shopsRunning vests and handhelds where a 500 mL flask rides in a front pocket
- Type
- Soft
- Capacity
- 0.5 L
- Weight
- 40 g
Packed size 26 x 9 x 5 cm Compare with a 2-litre bottle
About as long as a 2-litre bottle and about as wide as one. Drawn to scale.
Where to buy
Ultralight Outdoor Gear £22.99 In stock. Free delivery. Shop shows RRP £23.99.
View at shop: Ultralight Outdoor GearOsprey £24 In stock. Delivery £6. Osprey's UK shop. Its banner says free shipping over £75.
View at shop: OspreyPrices 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 9/10How much it adds to your pack for the water it holds. 9: Among the best you can buy for this.
Osprey UK lists 0.04 kg (40 g) for 0.5 L: 80 g per litre, under 100 g/L. Ultralight Outdoor Gear lists 42 g (84 g per litre), which bands the same. Osprey does not say whether its figure includes the removable WingStay stabiliser.
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
- Running vests and handhelds where a 500 mL flask rides in a front pocket
- A light spare bottle that packs down as it empties
- Hikers who want to add Osprey's UltraFlask filter cap (sold separately)
Strengths
- 40 g for 500 mL: 80 g per litre
- Removable WingStay stabiliser to stop bounce, even when empty (Osprey)
- 42 mm opening takes ice and drink mix
- High-flow, self-sealing bite valve and easy-grip twist cap
- TPU body with RF-welded seams
- Takes the UltraFlask filter cap (sold separately)
Weaknesses
- Osprey rounds its weight to 0.04 kg, and Ultralight Outdoor Gear lists 42 g
- Osprey gives no rolled-up size, so we cannot score packed size
- New for 2026, and 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.