Weight and pressure

Pressure change

On this page11

Where the cycles come from Which direction the failure goes The liner is what fails A plain cap beats a dispensing closure here Which is why the shelf is not a problem Headspace makes it worse Test it in a bag, not on a bench And then test it on its side, warm A bag is the belt to the closure's braces Which is the honest recommendation References

A plane, a pass and a hot tent. Three pressure cycles on one trip.

Where the cycles come from

A hold at altitude, a drive or a walk over a pass, and a pack left in the sun. Each changes the pressure inside a sealed container relative to outside it.

Which direction the failure goes

Both. Internal pressure pushes contents past a liner on the way up, and the partial vacuum on the way down draws air and sometimes water in.

The liner is what fails

Not the bottle and usually not the thread. 11 liners and sealing discs on this shelf, and the liner is the component nobody specifies on an order.

A plain cap beats a dispensing closure here

A flip top or a disc top has a moving part and a seal that works by being pressed shut. A continuous thread cap with a good liner is a simpler object with fewer ways to leak.

Which is why the shelf is not a problem

369 continuous thread closures against an archetype that asked for flip, disc, pump and mist. For a decant going in a pack, the plain cap is the better answer anyway.

Headspace makes it worse

Air expands and liquid does not, so a half-full bottle has more to push with than a full one. Filling a decant properly is a leak control.

Test it in a bag, not on a bench

Fill, seal, put it in a sealed clear bag, take it through a flight or a simulated altitude cycle and look at the bag. Anything that escaped is in the bag.

And then test it on its side, warm

Because a pack is horizontal as often as not and a tent in afternoon sun is hot. Those two together find the failures a pressure test alone misses.

A bag is the belt to the closure's braces

No closure is certain. A decant inside a small sealed bag is how experienced hikers carry anything that would ruin the trip, and it costs a gram.

Which is the honest recommendation

Buy the plain cap, specify the liner, fill it full, and bag it. Four things, none of which is a better bottle.

References

The archetype behind this shelf is store-liquid-decant: 15 to 120 mL, narrow mouth, flip top or disc top or lotion pump or fine mist, PET and HDPE, cold fill, thin, aqueous, poured, with "travel decant, leakproof under pressure change is the whole requirement" as its stated reason. All seven leaves sit on it, including fuel decant and fire starter, which are neither aqueous nor cold.

The Davis Pack Supply catalog, measured 18 October 2026. The camping and backpacking shelf is 979 rows: 453 containers and 526 closures. 15 mL to 500 mL with a median of 177; 8 containers at 15 mL or under, 27 at 30 or under, 86 at 60 or under, 189 at 120 or under, 394 at a pint or under. 201 PET, 126 HDPE, 76 PP, 50 glass. 221 bottles, 218 jars, 12 tubs and pails, 1 jug, 1 tube. 134 white, 114 clear, 66 natural, 52 amber. Closures: 369 continuous thread, 26 dome lids, 26 spouted, 19 flip top, 19 lug and twist, 18 child resistant, 11 liners and sealing discs, 9 phenolic, 7 spice caps, 7 buttress, 6 round tubs, and no disc tops, lotion pumps or fine mist sprayers.

Written from 40 CFR 152.500 and from the catalog as it stood on 18 October 2026. No log-reduction performance figures appear anywhere in this property, because the commonly cited numbers come from an EPA guide standard rather than a codified rule. Forest and park food storage orders are issued locally and are not summarized. Nothing here is a fuel bottle or a bear-resistant container.