Polypropylene

Polypropylene is cleared by the FDA for food contact as an olefin polymer under 21 CFR 177.1520, and it is made without bisphenol A or phthalates. BPA is a building block of polycarbonate and of epoxy can linings, not of PP, so a "BPA-free" claim on a polypropylene part is true but tells you nothing you did not already know. The genuine concern with PP is not a leaching monomer, it is particle release: the polymer surface degrades and sheds microplastic and nanoplastic fragments, most heavily in hot water. What that means for health is still open - the studies below measure exposure, not harm, and there is no established dose-response for ingested polypropylene particles. Ranking PP as one of the lower-concern food-contact resins is fair. Treating that as the same thing as inert is not.

Heat is what turns a polypropylene part into a particle source. Researchers at Trinity College Dublin, following WHO formula-preparation steps, measured PP infant feeding bottles releasing as much as 16.2 million microplastic particles per litre, with sterilisation and high-temperature water driving the release; polypropylene is roughly 82% of the global baby-bottle market. A 2025 study of polypropylene kettles found the first boil in a new kettle released on the order of 11.8 million nanoplastic particles per litre, falling more than 96% by the 150th boil, and hard tap water released fewer particles than ultrapure water. Two things follow. A new PP part in a hot path is at its worst when new, so break it in and discard the first few fills. And rinsing after sterilising, using water boiled in glass or steel, measurably cuts what ends up in the bottle.

Look for a 5 inside the chasing-arrows triangle, or the letters PP, moulded into the part. Unmarked, polypropylene is translucent to opaque with a waxy, slightly greasy feel and a living hinge that flexes thousands of times without cracking; it is one of the few common plastics less dense than water, so an offcut floats. The lookalike is HDPE (code 2), which also floats and also feels waxy but is stiffer and more opaque. Glass-clear parts that sink are more likely PET or a copolyester such as Tritan. If a spec sheet says only "BPA-free plastic", ask which resin, by code number, each water-touching part is, and whether that part sees water above 60 °C.

Top-rack dishwasher safe, and unbothered by kitchen acids and oils. What ages polypropylene is mechanical: scouring scratches, stress-whitening at flex points, and embrittlement under sustained UV if it lives on a sunny sill. A hazed, scratched or crazed PP part is worth replacing rather than scrubbing - the damaged surface is the part that sheds.

Code 5 is technically recyclable and curbside acceptance has improved, but the honest number is that the US recycled 8.7% of all plastics in 2018. Small unmarked parts - lids, tubing, scoops, water gauges - fall below the size and sorting thresholds at most facilities and go to landfill regardless of the code moulded into them.