Which resin, and what your formula does to it
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Cleaning products are among the most chemically aggressive things put into plastic bottles, and the bottle is not a neutral container.
The formula attacks the bottle
Solvents swell and soften some plastics. Strong alkalis and acids attack others. Oxidizers degrade several. Fragrance oils, which are solvents, migrate into the wall.
The result is a bottle that softens, crazes, panels, leaks at the shoulder, or lets the product evaporate through the wall over months.
None of it is visible on day one, which is why compatibility is established by testing rather than by the bottle looking fine after filling.
What each resin tolerates
HDPE is the workhorse. Good resistance to acids, alkalis and most aqueous formulations, poor clarity, and it can be permeable to some solvents and fragrances over time.
PET is clear and strong, and it is the one to watch: it is generally poor against strong alkalis and against some solvents, and a caustic formula in PET is a known failure.
PP handles heat well and resists many chemicals, and it is common for closures.
LDPE is flexible and used for squeeze formats, with similar chemistry to HDPE.
Glass is inert to essentially everything, and it breaks and is heavy.
Fluorinated HDPE exists for solvent-bearing products where permeation is the problem.
How failure shows
Paneling, where the bottle collapses inward as headspace pressure drops or the wall is attacked.
Swelling or bulging, from pressure or from the wall absorbing solvent.
Crazing, a network of fine cracks, usually from solvent stress.
Weight loss, which is product permeating out through the wall and is invisible until you weigh it.
A seeping shoulder or neck, which is usually the closure liner rather than the bottle.
Testing it rather than assuming
Fill six bottles with the actual formula, cap them as they will be sold, and keep them: some at room temperature, some warm, some in a hot place.
Weigh them at the start and at intervals. Weight loss is the earliest quantitative signal and it shows long before anything is visible.
Three months minimum, and longer if the product has a long shelf life.
Ask the supplier for chemical compatibility guidance too, and treat it as a starting point rather than an answer, because it describes the resin and not your formula.
The resins we stock, and what a cleaner does to each
