How full to fill it
Updated
A small decision that decides whether parcels arrive dry.
Why not to the brim
Liquid expands with temperature. A bottle filled to the neck at 18 degrees is pressurized at 40, which is a delivery van in summer.
Pressure pushes past the liner, and a case of leaking bottles is a total loss plus a cleaning job plus a customer.
Headspace is the room that expansion needs.
Temperature and altitude
Air freight and mountain roads both drop the external pressure, which makes the headspace expand against the closure.
A bottle that is fine in a van can weep on a plane, and a product that ships nationally sees both.
Which is an argument for slightly more headspace than looks ideal, and for testing a capped bottle warm before committing to a fill level.
Consistency
Fill to a weight rather than a line, and check through the run.
A visible difference in fill level between two bottles on a shelf is something a buyer notices and a maker does not, because the maker sees them one at a time.
And the declared net quantity has to be right, which is the compliance version of the same point.
The trigger case
A trigger sprayer has a dip tube that occupies part of the bottle, so the effective headspace is smaller than it looks.
The tube also has to reach the base to empty the bottle, and has to not kink, which is a length specification rather than an approximation.
Fill so that the tube sits in liquid when the bottle is upright, or the first user pulls a dry trigger.