Chemical resistance is the whole decision
Updated
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What the shelf holds
A hundred and ninety-one containers from 100 ml to about 4.7 liters, of which 149 are HDPE and 42 are glass, with 236 closures. The common neck finishes are 38-400, 24-410 and 28-400. There is no PET on this shelf, and that is the constraint working rather than a gap in what we stock.
HDPE for the working containers
It resists the solvents and the amine hardeners this craft involves, it does not shatter when dropped on a workshop floor, and it is cheap enough to treat as semi-disposable. For decanting, for storage and for anything that gets handled daily it is the right answer.
Glass where you need to see it or keep it
Inert to effectively everything here, and you can see the level and the color without opening it. The cost is weight and breakage, and a broken bottle of hardener is a cleanup with an exposure attached rather than a mess.
Why PET is absent
It is the workhorse of the food properties and it is not the right material against solvents and amines over time. The archetype excludes it, and an empty PET bottle from another job is not a container to decant hardener into.
Check the specific product, not the category
Resin systems vary and so do the solvents people keep alongside them. Section 7 of the safety data sheet covers handling and storage and will say if a material is unsuitable. The shelf narrows the field; the data sheet settles it.
The liner matters as much as the bottle
A chemically appropriate bottle with the wrong liner leaks or contaminates through the cap, and that is the next page.