"Chemical resistant" is meaningless without naming the chemical
Plastic chemical-resistance charts are built around specific named substances, not a general "chemicals" category, because plastics respond very differently to a mild cleaner than to a solvent like acetone. A part that handles soap and water fine can soften or craze on contact with certain solvents in minutes. This tool refuses to guess when the chemical is not named: selecting "unknown" routes you to identifying the exact substance and checking its safety data sheet, rather than returning a false sense of confidence.
How the screen works
For a named chemical, a general compatibility rating (good, caution, or poor) is looked up for your chosen material, based on widely available plastic chemical-resistance references. Sustained contact escalates a "caution" rating to "poor" for planning purposes, since duration is one of the biggest factors in real chemical attack. An unnamed chemical always returns a routing result rather than a guessed rating.
Worked example
Acetone against PETG with occasional contact returns a caution rating, since PETG has partial resistance to acetone that degrades with more exposure; switching to sustained contact in the same scenario escalates this to a poor rating and recommends either switching material (Nylon generally resists solvents better) or eliminating the exposure.
A common mistake
A frequent error is assuming a "resistant" rating means indefinite exposure is fine. Even a generally compatible material and chemical pair can degrade slowly with months of continuous contact, especially at elevated temperature. A rating here describes typical short-to-medium term behavior, not a lifetime guarantee; for a long-service part, periodic inspection matters even after a favorable initial screen.
Limitations
This is general planning guidance for common chemical categories at typical household concentrations, not a substitute for the specific product's safety data sheet or your material supplier's own chemical-resistance chart. Concentration and temperature both change real-world results significantly; test a real sample under real conditions for anything safety-relevant.