ULTRA RUNNING BOTTLES, CUPS AND SOFT FLASKS

Start with the race rules and the longest period you expect to spend between reliable water supplies. Many 50 and 100 mile events specify capacity for around one litre as part of the mandatory kit, but that is a minimum requirement rather than a prediction of how much you will actually need.

Temperature, exposed terrain, climbing, pace and personal drinking habits can all increase the requirement. A slower runner may spend considerably longer between the same two checkpoints than a faster runner and therefore need more fluid for that section.

In hot conditions it can be sensible to refill whenever a dependable opportunity appears rather than running past a tap or aid station because your calculated plan says you should still have enough. Ultra running rarely goes exactly to plan, and carrying some contingency can become more appealing as experience and race duration increase.

No. A requirement to carry one litre normally specifies the amount of fluid capacity, not how that capacity must be divided. Subject to the race rules, it might be carried in two 500ml front flasks, larger bottles, a reservoir, additional flasks elsewhere in the pack, or a combination of carrying methods.

Two 500ml soft flasks are common because many running vests are designed around them, but they are not automatically the best arrangement for every runner or event. Decide how much fluid you need first, then work out where and how you want to carry it.

Long gaps between aid stations, hot weather, remote terrain or a higher mandatory capacity can justify carrying more than one litre. Some running vests are designed to accept taller 600ml to 800ml flasks at the front or sides, while another option is to add a reservoir or carry an additional flask elsewhere in the pack.

Extra capacity does not necessarily need to be filled for the entire race. A spare flask can provide flexibility for a particularly long or hot section without committing you to carrying the additional weight from start to finish.

Not necessarily. Two flasks with the same 500ml capacity can have different widths and heights. Some manufacturers design vest pockets around a particular flask shape, so a replacement from another brand may sit too high, be too wide or disappear too far into the pocket as it empties.

Check the flask width and the distance from its base to the shoulder against the pocket you intend to use. This becomes particularly important with 750ml, 800ml and other higher-capacity bottles, which are usually taller than standard 500ml flasks and generally work best with a vest specifically designed to support them.

Retention bungees around the upper part of the flask can also help prevent a soft bottle dropping down inside the pocket as its volume reduces.

A fully soft flask compresses as you drink. Removing the air reduces fluid movement and sloshing, and the bottle takes up less space as it empties. The compromise is that very soft flasks can lose their shape, sink into a vest pocket and be less convenient to handle or refill.

A semi-rigid or hybrid bottle retains more of its shape, which can make it easier to hold, stand on an aid-station table and return to the same position in a pocket, while still requiring little effort to squeeze when drinking.

Neither approach is automatically better. Some runners value maximum collapsibility and silence; others prefer a bottle that stays predictable as the contents reduce. Try both in training if the distinction matters to you.

Yes. A wide opening makes rapid refilling easier and gives you more room when adding electrolyte or carbohydrate powder without spilling it around an aid station. It can also make the bottle easier for a volunteer to fill.

Cap diameter and grip matter as well. Small caps can become difficult to remove if they have been overtightened to prevent leaks, while a larger cap with useful grip can be easier to open with tired or cold hands.

Bigger is not automatically more comfortable, though. A bulky or heavily ridged cap can press against the chest depending on where the flask sits. As with many ultra-running choices, the practical answer depends on the runner, vest and position of the bottle.

A locking valve provides extra reassurance that fluid will not escape when the flask is compressed in a pocket or packed alongside other equipment. This can be particularly useful when you want certainty that a bottle containing sports drink or concentrated nutrition will stay closed.

It is still important to close the main cap correctly and check the system before race day. A locking valve solves one potential source of leakage rather than making poor fitting or damaged components irrelevant.

A straw can make drinking easier when the top of a front flask sits below your mouth and can reduce the amount of neck movement needed to reach the valve. Some tubes can be shortened to suit the runner and vest.

The compromise is additional tube and valve hardware. Check that your vest has a suitable retaining loop or strap so the straw does not move around in front of you while running. A shorter straw may work without additional retention, but this is another preference worth testing before an event.

Yes, provided the particular flask and valve are suitable for what you intend to carry. Standard soft bottles work well for water, electrolyte drinks and carbohydrate mixes, while smaller nutrition flasks can be useful for carrying concentrated energy gel or other thicker liquid fuel.

A wider opening is particularly useful when adding powder at an aid station because there is more room to pour cleanly. Very viscous nutrition may require a valve or cap specifically designed for thicker contents rather than a standard hydration bite valve.

Empty and clean the flask after use, particularly when it has contained carbohydrate drink, electrolytes or concentrated nutrition, then allow it to dry properly before storage. Soft flasks cannot normally be turned completely inside out in the way some hydration reservoirs can, so drying takes a little more care.

Discolouration with age does not necessarily mean a flask is dirty, but soft bottles are wear items. Many runners eventually replace them when they no longer look or feel clean, or when the material, seams, valve or cap begin to show deterioration.

Pinholes and other damage can occur, particularly over repeated long-distance use. If losing a flask would leave you without enough hydration capacity for an important section, carrying some redundancy is worth considering.

No. Check compatibility before buying a replacement cap, valve or drinking tube. Thread diameter and cap size vary between flask systems, so an accessory from the same underlying manufacturer does not automatically fit every bottle it produces.

When replacing a component, match it to the specific flask or confirm the relevant thread or cap diameter rather than choosing by appearance alone.

Many races are now cupless and require runners to provide their own drinking cup at aid stations. A collapsible soft cup packs down small enough to remain in a race vest, waist pack or pocket and is intended for drinking at checkpoints rather than carrying water between them.

Always check the current race rules. A reusable cup is a separate piece of equipment from your required fluid-carrying capacity unless the organiser specifically states otherwise.