Fill temperature and the container

The pour temperature is a formula decision and a container decision at the same time, and the container usually sets the ceiling.

Two ceilings

The formula wants to be poured above its setting point and below the temperature at which it loses flavor or oxidizes.

The container has its own limit, and on a thin polypropylene tube that limit is lower than people expect. Whichever is lower wins.

What a hot fill does to a plastic tube

It softens, the barrel goes slightly oval, and the mechanism that was smooth becomes stiff.

Or it shrinks a little on cooling and grips the disc. Either way the fault appears after the balm has set, so a whole run can be affected before anybody winds a tube up.

Most lip balm formulas pour comfortably below any sensible tube's limit, so this is rarely a live problem, but it becomes one with a carnauba-heavy summer formula, which needs a hotter pour than a soft beeswax one.

Metal and glass

A tin or a glass pot takes any temperature you would pour at, which removes the ceiling.

What they add instead is thermal mass: a cold metal tin chills the balm on contact and can set the outside before the middle, which is its own defect. Warming tins slightly before filling is worth testing.

Finding your number

Pour a row at three temperatures across the plausible range, let them set, then wind each fully up and down, twice, a day later.

That test takes ten minutes, costs six tubes, and catches a fault that otherwise ships. Record the number with the formula rather than in your head.

References