Leaving bottles in a hot car
Severe impactCabin temperatures of 60–70°C, sustained for hours or weeks.
The short answer
A parked car in summer is the hottest place a plastic bottle will routinely sit, and duration compounds temperature. A bottle that had one warm afternoon is fine. A multipack that has lived in the boot since June is the realistic worst case, and a sealed cap does nothing about it because the migration comes from the inside of the bottle wall.
Why it happens
- Interior air routinely reaches 60–70°C on a summer day; surfaces in sun go higher
- Release rises with both temperature and time, and the two multiply
- UV through glass adds photodegradation on top of heat
- Sealing prevents contamination getting in, not migration from the wall
The fix, easiest first
- Do not use a car as a pantry — keep cases indoors
- Carry filtered water in stainless steel instead
- If it tastes of plastic, tip it out; that flavour is the signal
- Never refill and re-heat a single-use bottle
Packaging this applies to
PET plastic bottle
Polyethylene terephthalate, PET (#1)
HDPE bottle or jug
High-density polyethylene, HDPE (#2)
Find which habit is costing you most
MicroPlastics scores the ingredient list, the packaging and how you actually use a product, then names the single cheapest change.
Get my exposure scoreFrequently Asked Questions
Is it safe to drink water left in a hot car?
A parked car in summer is the hottest place a plastic bottle will routinely sit, and duration compounds temperature. A bottle that had one warm afternoon is fine. A multipack that has lived in the boot since June is the realistic worst case, and a sealed cap does nothing about it because the migration comes from the inside of the bottle wall.
Why does this happen?
Interior air routinely reaches 60–70°C on a summer day; surfaces in sun go higher. Release rises with both temperature and time, and the two multiply. UV through glass adds photodegradation on top of heat. Sealing prevents contamination getting in, not migration from the wall.
What should I do instead?
Do not use a car as a pantry — keep cases indoors. Carry filtered water in stainless steel instead. If it tastes of plastic, tip it out; that flavour is the signal. Never refill and re-heat a single-use bottle.
Sources
- Earth Action with rePurpose Global (2026). Microplastic migration from food and beverage packaging (reported May 2026). Forbes.
- Qian N, Gao X, Lang X, et al. (2024). Rapid single-particle chemical imaging of nanoplastics by SRS microscopy. Proceedings of the National Academy of Sciences (PNAS).
- Winkler A, Santo N, Ortenzi MA, et al. (2022). Does mechanical stress cause microplastic release from plastic water bottles?. Water Research.
- Hernandez LM, Xu EG, Larsson HCE, et al. (2019). Plastic teabags release billions of microparticles and nanoparticles into tea. Environmental Science & Technology.