The 500ml Soft Flask is the general-purpose option with a wide 42mm opening for straightforward refilling. The 300ml Soft Flask is more compact and uses a narrower 28mm opening, making it useful where a smaller bottle or pocket is preferred.
The 625ml Soft Flask increases capacity without stepping up to the larger 800ml size. It uses a low-profile 28mm locking cap, making it a useful choice when you want more than 500ml but do not need a wide 42mm opening.
The 800ml Soft Flask provides greater capacity with a wide 42mm opening and locking cap. The 1 Litre Soft Flask takes capacity further and uses slightly thicker material to support the larger volume and provide greater durability. Its flatter base and relatively parallel sides also give the filled flask a more defined shape.
Fit becomes increasingly important as capacity increases. Check the available pocket height, width and retention rather than assuming that a pocket designed around a 500ml flask will accommodate the larger options.
