I bought a stainless steel bottle with a plastic liner last year, and no matter how much I scrub it or use baking soda, there's this persistent chemical smell. I've tried vinegar soaks and everything. Is the plastic breaking down or leaching something, or am I just being paranoid?
Don't assume it's just paranoia or ignore it - that plastic liner smell after a year is likely the polymer degrading from repeated temperature changes and use. The good news is you're probably not in danger from occasional exposure, but if the smell won't go away even after thorough cleaning, the liner's integrity is compromised and it's time to replace the bottle or switch to one that's fully stainless steel inside.
The plastic liner is genuinely breaking down. Those polymers weren't meant to handle constant temperature swings from hot water fills and cold storage, especially over a full year of daily use. The smell you're catching is volatile organic compounds (VOCs) being released as the material degrades. You're not paranoid - your nose is picking up a real chemical process.
Here's the thing though: most people focus on cleaning the bottle itself, but they miss that the liner is the source. Scrubbing and baking soda won't help because the degradation is happening inside the polymer structure, not on the surface. What actually works is getting the bottle to off-gas faster. Leave it uncapped in direct sunlight for a few hours a day for a week or two. Heat and UV light accelerate the release of those compounds, and then they just dissipate. Some folks also report success running it through the dishwasher on high heat repeatedly, though that can speed up further degradation.
The real pitfall is that once a plastic liner starts breaking down, you're fighting a losing battle. Even if you get the smell mostly gone, it'll come back. If you want this bottle long-term, you might consider replacing it with one that's fully stainless steel inside, or switching to glass. A decent stainless steel bottle without a lining usually costs about the same as what you spent on that one and actually lasts.
If you've had it for a year and you're actually smelling something distinct rather than just remembering the new bottle smell, the plastic liner is likely degrading - those polymers deteriorate faster than people expect when cycling through temperature extremes.
The catch is that a stainless steel exterior with a plastic interior kind of defeats the purpose, so if this keeps bothering you, a fully stainless or glass bottle would be a cleaner investment since you're clearly someone who maintains their gear well.
I had a similar issue with a bottle I used on shift at the station - kept it in the truck and it got exposed to wild temperature swings, hot days in the cab, then the cooler nights. After about a year, that chemical smell got stronger no matter what I did. Turns out those plastic liners in stainless steel bottles can degrade pretty quickly when they're constantly going from hot to cold. The material just breaks down over time.
The plastic itself is probably fine in terms of leaching anything harmful into your water at this point - you're mostly just smelling the degradation, kind of like how old plastics in a garage smell musty and weird. But if the smell is bugging you (and I get it, it would bother me too), your best bet is honestly just replacing it. These liners aren't usually meant to last more than a couple years with regular use, especially if you're filling it with hot water or leaving it in a hot car. Some people try rubbing the inside with baking soda paste and letting it sit overnight, then rinsing really thoroughly, but once the smell's that embedded, you're fighting an uphill battle. Might be worth grabbing a new bottle or switching to a standard stainless steel without a plastic liner if you want something that'll last longer.
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