Reusable water bottles and travel mugs: what's really inside

Buying a reusable bottle is the easiest plastic swap there is. It’s also a little ironic. Plenty of “reusable” bottles are plastic. Many metal ones hide a plastic lining. Nearly all of them have a plastic lid. And a surprising number of the shiny steel ones are sealed with a dot of lead.

None of that means you should go back to single-use bottles. It means you should know what you’re holding. Here’s what’s inside, what the evidence says about each part, and how many refills it actually takes to come out ahead.

Aluminium bottles and the liner problem

Aluminium is light and cheap, but it reacts with acidic drinks, so aluminium bottles are coated on the inside. For years that coating was often an epoxy resin, the same family of plastics that lines food cans and is made with BPA. (Our BPA explainer covers why that matters.)

That’s the backdrop to the most embarrassing moment in reusable-bottle history. In the late 2000s, the Swiss maker SIGG’s aluminium bottles were sold to people trying to get away from polycarbonate and BPA. Then, in 2009, SIGG’s CEO wrote to customers that bottles made before August 2008 had an older water-based epoxy liner containing trace amounts of BPA. Bottles made since then had a new BPA-free liner the company called EcoCare. The letter said SIGG had begun developing that liner in June 2006, partly because of questions about BPA, and maintained that the older bottles had been tested and leached no BPA. In other words, SIGG had been working on a replacement for about two years before the switch, and told customers about the old liner only in 2009, while many were buying its bottles specifically to avoid BPA.

The Environmental Working Group accused SIGG of having led consumers and retailers to believe its products were free of BPA, and demanded refunds rather than SIGG’s offer of an exchange for another SIGG bottle.

Did old epoxy liners actually leak BPA into water? An independent 2011 study tested several types of reusable bottle. It found BPA migrating from epoxy-lined aluminium bottles at levels that varied by manufacturer, with the worst reaching about six times the highest level from polycarbonate bottles. Boiling water made it significantly worse. The study didn’t name the brands it tested, so it isn’t a verdict on SIGG’s old liner. It found no detectable BPA from uncoated stainless steel, from Tritan plastic, or from aluminium with the EcoCare liner.

The lesson outlasts the scandal. A liner is a coating you can’t see, made of something you usually aren’t told. “BPA-free” tells you what one chemical isn’t in it, not what is. Our product standard rejects any food or drink coating the maker won’t name.

“Ceramic-coated” interiors

The newest selling point on steel bottles is a “ceramic” inner coating, pitched as keeping coffee tasting like coffee. It’s usually not ceramic in the mug sense. It’s a thin coating sprayed onto the steel, and makers rarely say what it is made of.

We found no peer-reviewed study of what migrates or flakes out of these coatings in drink bottles. The closest evidence comes from “ceramic” nonstick pans, which use a similar silica-based (sol-gel) coating. Researchers found particles could come off those coatings under heat, acid and scratching, as we cover in our nonstick pans explainer. A bottle isn’t a frying pan, so that’s an analogy, not evidence.

The practical point: uncoated stainless steel has a long track record and no coating to wear through. A coating is one more material you have to take on trust. If you want one anyway, look for a maker that names the material and says how it was tested.

Lead in vacuum-insulated bottles: the sealing dot

Double-walled “vacuum-insulated” bottles and tumblers keep drinks hot or cold because the air between the two steel walls has been pumped out. That gap has to be sealed, usually through a small hole in the base. The traditional way is to melt a pellet of solder over it, and that solder has often contained lead.

In early 2024, after TikTok users started swabbing their tumblers with home lead tests, Stanley confirmed it uses this method. Its support page said (in an April 2025 archived copy) that the vacuum is sealed with pellets, “some of which include some lead”, covered with a durable stainless-steel layer so that consumers can’t reach them. The company says no lead is on any surface that touches you or your drink. If the base cap comes off in ordinary use, it says the product may be covered by its lifetime warranty. Stanley’s spokesperson called the pellet “industry standard”, so this isn’t one brand’s quirk.

How worried should you be?

Precision matters here, because this story produced a lot of panic and a lot of shrugging.

• The lead isn’t in your drink. The dot sits on the outside of the base, under a steel cap, sealing the vacuum gap. Your coffee is inside the inner wall, on the other side of that gap. There’s no route for it to dissolve into a drink in an intact bottle. Nobody we found has shown lead migrating into the contents.
• The risk starts if the cap comes off. As Jane Houlihan of the nonprofit Healthy Babies, Bright Futures told CNN: “If the cup stays intact, there’s likely no lead exposure risk for consumers. But if that bottom seal comes off, all bets are off.” An exposed dot can rub off onto hands, and small children put cups and hands in their mouths.
• That isn’t hypothetical for kids’ cups. US regulators recalled about 10,500 toddler bottles and cups because the base could break off and expose a solder dot containing lead. The maker had seven reports of the base breaking off, and no injuries. In late 2023, four brands of children’s steel cups sold on Amazon were recalled because the bottom had an accessible solder bead with lead above the federal limit. The biggest of them was about 84,000 cups; parents were told to take them away from children and contact the seller for a refund. Separately, about 346,000 children’s steel cups from another brand were recalled in 2023 for lead above the federal limit.

Why take a dot seriously at all? Because, as the WHO puts it, no level of exposure to lead is known to be without harmful effects, and children are the most vulnerable.

So the honest summary: an intact adult tumbler is not a meaningful lead source. A damaged one, or a cheap kids’ cup with an exposed bead, can be. A vacuum bottle that relies on nobody ever dropping it is a design choice, not a law of physics.

Plastic lids, straws and spouts

Even an all-steel bottle usually has a plastic lid, and that’s where your mouth goes. Polypropylene, Tritan and silicone are the usual suspects, alongside flip spouts, bite valves and built-in straws.

Lids matter for two reasons:

• Wear. In tests on single-use bottles, opening and closing them visibly increased plastic particles on the surface of the caps, most strikingly after 100 openings, with big differences between brands. A sports-bottle lid gets opened thousands of times.
• Heat and soap. A 2022 study of reusable plastic sports bottles found more than 400 plastic-related compounds migrating into water, including plasticizers, antioxidants and photoinitiators; the authors flag the photoinitiators for possible hormone-disrupting effects. Running the bottles through the dishwasher increased leaching, and over 400 dishwasher-related compounds were still coming out after the bottles had been rinsed. That study was of whole plastic bottles, but lids are the same kinds of plastic, put through the same dishwasher.

Silicone isn’t a free pass either. Steam-sterilising silicone baby-bottle teats released micro- and nanoparticles in one study; the health effects are unknown. That’s why our standard allows a small silicone seal touching a drink only in products we call “plastic-minimal”, never “plastic-free”, and always names it.

What to look for: a lid where your drink and your lips touch steel or glass, with any plastic outside the drink path. Swap built-in plastic straws for steel or glass ones. If you have a plastic lid, keep it out of the dishwasher’s hottest cycle and replace it once it’s scratched or cloudy.

Tritan and the “BPA-free” fight

Tritan is a copolyester plastic launched by Eastman Chemical in 2007 as a shatterproof, clear replacement for polycarbonate. It doesn’t contain BPA, and the 2011 study above found no BPA coming out of it. The fight is over whether it releases other chemicals that act like estrogen.

In 2011, a team led by University of Texas neurobiologist George Bittner tested 455 plastic food-contact products with a sensitive cell assay. Over 70 percent leached chemicals with detectable estrogenic activity even without any stress, and the authors concluded that almost all the plastics they sampled did, especially after microwaving, UV light or sterilising. Some BPA-free products released more estrogenic activity than the BPA-containing ones they replaced. A 2014 follow-up on 50 BPA-free replacement products found that many made from acrylic, polystyrene, polyethersulfone and Tritan leached estrogenic chemicals, including baby products, often more after UV exposure. Some products made from other resins showed none.

Two conflicts of interest sit on opposite sides. Bittner founded CertiChem, which sells testing, and PlastiPure, which sells its own “EA-free” plastic. On the other side, a 2012 study supporting Eastman’s position found Tritan’s three building-block chemicals showed no estrogenic or androgenic activity across a battery of tests. That tested the monomers, not finished bottles after years of sun and dishwashers.

Then it went to court. Eastman sued PlastiPure and CertiChem over a sales brochure that showed Tritan products with significant estrogenic activity. A jury in federal court in Texas found the brochure was false advertising, and in December 2014 a federal appeals court upheld an injunction barring the companies from claiming in their marketing that Tritan leaches significant estrogenic activity.

Read that ruling carefully, because both sides spin it. It was about statements in commercial advertising, made to customers without the data and context of a scientific paper. It didn’t retract the peer-reviewed studies. The court said the researchers “may continue to pursue their research and publish their results.” A jury was persuaded on the ads. Science hasn’t settled the underlying question, and no independent group has produced a decisive study either way.

Our take: “BPA-free” plastic means one chemical is absent, not that the plastic is inert. Our product standard doesn’t list Tritan or any other plastic touching your drink or mouth, and the Tritan fight is a good illustration of why.

Stainless steel: the default for a reason

Food-grade stainless steel, usually labelled 18/8 or 304 (or 316 for slightly better corrosion resistance), is what most of the evidence above keeps landing on. It needs no lining, and in the 2011 study it released no BPA.

It isn’t perfectly inert. Steel pots used to simmer tomato sauce for hours released nickel and chromium into the sauce, most from new pans, falling off after about six cooking cycles. That matters mainly for people with nickel allergy. A bottle of cold water is a far gentler test than six hours of hot, acidic sauce, but if you’re nickel-sensitive, avoid storing acidic drinks in a new bottle for long periods.

Glass is the other inert option: nothing to leach, but heavier and breakable, and usually wrapped in a silicone sleeve.

Kids’ bottles: where the red flags cluster

Children’s drinkware combines every issue above: cheap steel cups from little-known sellers, plastic spouts, silicone straws and hard-to-clean valves. And kids chew, drop and mouth everything.

Red flags:

• A visible bead or dimple on the outside base of a double-walled steel cup, or a base cap that’s loose, cracked or gone. That’s the profile of the recalls above.
• No lead statement. For any vacuum-insulated kids’ cup, look for the maker to say whether the seal is lead-free and how it’s enclosed.
• Valves and straws you can’t take apart. They trap milk and juice.
• Little-known marketplace brands. The four late-2023 recalls above were all children’s cups sold on Amazon by little-known brands.

For toddlers, a plain single-wall steel cup with no insulation has no sealing dot at all. More on kids’ products in our baby and kids section and our article on microplastics in baby bottles.

Cleaning and mould

The least glamorous risk in your bottle is also the most common: whatever is growing in it. A bottle that only ever holds water still collects mouth bacteria, and the lid gasket and spout stay damp.

The evidence is limited but consistent. A citizen-science swab of one reusable bottle turned up a Klebsiella strain resistant to several antibiotics and able to form biofilms on plastic. In a study of 30 everyday bottles, plastic (PET) bottles carried about twice the bacterial load of stainless steel ones, and cleaning cut it sharply. A 2026 study found that dishwashing reduced microbial load by about 90% compared with not washing. These are small studies, and nobody has measured how often a dirty bottle actually makes people ill. But “rinse occasionally” isn’t a cleaning routine.

What works: wash daily with hot soapy water and a bottle brush. Take the lid apart and pull out the gasket. Clean the spout or straw with a straw brush. Let everything dry fully, open, before reassembling. Steel bodies can go in the dishwasher if the maker allows it (check the outside paint and the base cap). Plastic lids are better washed by hand, for the reasons above. Bin a gasket with black spots you can’t scrub off.

How many uses before a reusable wins?

A reusable bottle or cup takes far more material and energy to make than one disposable, so it starts in debt. Each refill pays some of that back, and each wash adds a little. The question is how fast you break even.

• Bottles. In a 2026 life-cycle study, making one 500 mL PET bottle produced 0.0925 kg of CO2-equivalent, against 13.1 kg for a 1-litre aluminium bottle and 0.28 kg for a reusable HDPE plastic one. On those production figures alone, the aluminium bottle needs to replace about 140 PET bottles to pay off its manufacture (our arithmetic). Over a year of drinking a litre a day away from home, the 730 PET bottles came to 67.5 kg, and the reusables’ production became negligible. How you washed them mattered most.
• Cups. A UN Environment Programme review of life-cycle studies found reusable cups beat single-use cups on climate after anywhere from 10 to 670 uses, depending on the materials, what happens to the disposables, and especially washing. One study it summarised found a stainless steel cup beat all the single-use plastic cups after 140 uses. The review found the break-even point was always within the reusable cup’s expected lifespan. It also found paper cups could come out ahead on climate if more than 80% were recycled, which it notes is seldom achieved.
• Washing changes everything. A 2026 Korean study of steel tumblers found the break-even point against the average of a paper and a PET cup was 17 to 19 uses with a cold-water hand wash, 45 with a household dishwasher, and up to 90 with a hot-water hand wash using a lot of water. A dedicated electric tumbler-washer, as modelled, never broke even at all.

Two caveats. These studies mostly measure climate impact. They don’t count plastic litter or microplastics, which are the main reasons to avoid single-use bottles and which make the case for reusables stronger. And every number assumes you keep using the thing. A tumbler bought as a fashion item and replaced every season, or the fifth free bottle in the cupboard, never pays off. The greenest bottle is the one you already own.

What to do, ranked by evidence

1. Use the bottle you have, a lot. The life-cycle evidence is strongest here. Reusables win only with repeated use, so don’t collect them.
2. Choose plain stainless steel or glass where the drink sits. Uncoated steel released no BPA in independent tests and has nothing to wear through. Avoid unnamed liners and coatings.
3. Keep plastic away from your mouth and your hot drinks. A steel or glass drinking surface beats a plastic spout. If you have a plastic lid, hand-wash it and replace it when it’s worn. The evidence on lids is moderate and comes mostly from whole plastic bottles.
4. Check the base of vacuum-insulated bottles. If the cap is missing or loose, stop using it, especially around children, and claim a replacement. For kids, prefer cups whose maker states the seal is lead-free, or uninsulated single-wall steel. The recall evidence is solid. The risk to adults from intact bottles is low.
5. Clean it properly. Daily wash, lid apart, dry open. The evidence is small studies, but it’s cheap and obvious.
6. Treat “BPA-free” as a starting point, not a safety claim. The estrogenic-activity evidence is contested and comes with conflicts on both sides. Stepping off plastic sidesteps the argument.

For how we vet bottles and cups before listing them, see our standards. More in our on-the-go section.