Closures for pressure
Updated
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The lined screw cap
124 of the 176 closures here are continuous thread. A liner compressed against the land by the thread gives a distributed, mechanically maintained seal, and it is the most pressure-tolerant option on this shelf.
The flip top
Fifteen of them, and they are what customers want: one-handed, no cap to lose. The seal is a small snap fit over an orifice, which is a much smaller area holding the same pressure difference.
The spout
Twenty-five spouted closures. Good for controlled pouring into a smaller container and another small sealing area. For a decant that will be carried rather than used at a sink, it is a comfort choice with a cost.
So the honest recommendation
Ship with a lined screw cap for travel and offer a flip top for home use, or supply both. Selling a flip top as a travel closure without testing it is where the complaints come from.
The liner is doing the work, so specify it
Of the 176 closures, 56 carry an HIS induction-seal liner, 29 a pressure-sensitive liner, 14 F217, 13 PE foam and 13 foam, and 21 carry none at all. A closure with no liner on a thin liquid is the wrong starting point.
An induction seal is a single-use answer
It is an excellent barrier and the customer breaks it on first use, after which the screw cap and its liner are doing everything. For a refillable travel bottle it protects the first journey only.
Torque matters and nobody measures it
A cap run down by hand varies enormously, and an under-torqued cap on a pressure-stressed bottle is the commonest single cause of a leak. For a product you fill yourself, a consistent process is worth more than a better closure.