Capacity decides the use case, so it's the first thing to settle when you order a custom soft_flask. Here's what each size range is typically used for, and why the dimensions matter as much as the volume.
150–250ml
The small sizes suit energy gels, electrolyte concentrate, and short runs, and they're the usual choice for event race cups. Sports-nutrition brands tend to order in this range. For thick gels, specify a wider mouth so the flask is easy to fill and clean — see our note on energy gel flasks.
350–500ml
This is the everyday running size and the one most hydration vests are cut for. Vests commonly carry two 500ml flasks in the front pockets, which spreads the weight across the chest. If you're building a general hydration line, this range covers the most customers.
600–1000ml
Larger flasks suit longer efforts and hiking, where runners want fewer refills. The trade-off is that big flasks are harder to seat in a standard vest pocket, so check the fit before committing.
Dimensions Matter as Much as Volume
A flask has to fit the vests and belts your customers already use, so confirm height and width against the target pocket rather than ordering on capacity alone. As a reference point, a 400ml flask around 29 × 8.5 cm sits in the middle of the range that fits most standard vest and belt pockets.
Next Steps
Capacity is one decision in the wider soft_flask sourcing process. The R50044 is 400ml at 29 × 8.5 cm as standard, with other sizes from roughly 150ml to 1000ml — contact us to match a size to your use case.