Thermos · Insulated Drinkware Tumblers
Thermos Stainless Steel Tumbler Slide Lock Lid
Lower concern. Stainless steel core is PFAS-free; lid material unclear.
Thermos tumblers use stainless steel bodies, which do not require PFAS. The slide lock lid material composition is not publicly disclosed, introducing minor uncertainty about any coatings or gasket treatments.
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Stainless steel body, plastic/silicone lid
Brand disclosure
Brand is silent on PFAS
Lab data
No public lab test
Why this grade
Uncoated safe material
Bare, uncoated material (cast iron, stainless, carbon steel, or glass) with no surface treatment to contain PFAS.
Category baseline
other is a category where PFAS exposure is more common.
No PFAS disclosure
No public statement about PFAS in this product.
The full breakdown
What it's made of and why it matters
The Thermos Stainless Steel Tumbler's primary containment surface is food-grade stainless steel, which does not leach metals or degrade into drinking water under normal use. The removable plastic and/or silicone lid is the secondary contact point; silicone resists heat and chemical leaching better than hard plastics, but the exact composition (whether virgin polymer, recycled content, or elastomer blend) is not publicly detailed by Thermos. The "Slide Lock" mechanism is typically polycarbonate or acetal copolymer, materials that are stable at room temperature but should not be exposed to boiling water.
The brand's record and disclosure
Thermos does not publish detailed material safety disclosures or third-party certifications (such as BPA-free labeling or FDA compliance statements) on their product pages for this tumbler. The company has no documented history of recalls or safety controversies related to this specific product line. Thermos is owned by Groupe SEB, a large housewares manufacturer, but neither parent nor subsidiary provides transparency on polymer sourcing, BPA alternatives used in lids, or testing protocols for leaching.
How it compares in its category
Stainless steel tumblers are among the safest reusable drinkware options because the steel itself does not degrade or leach. However, competing brands (Hydro Flask, S'well, Contigo) often explicitly market lids as BPA-free or publish material data sheets; Thermos does not. Most stainless steel tumblers in this price range use similar silicone or plastic lids, so differentiation is minimal on safety grounds. The Thermos brand trades on durability and temperature retention rather than material transparency.
If you buy it
Do not pour boiling water directly onto the plastic lid; allow hot beverages to cool slightly or fill from the side. Hand-wash the lid and tumbler separately; dishwasher heat can degrade plastic components over time. Replace the lid if it becomes cloudy, cracked, or develops odor, as these signs indicate polymer degradation. If you prefer explicit BPA-free or material certifications, contact Thermos directly or choose a competitor that publishes those details.
Beyond PFAS: other things we checked
Established hazard classes for this product type, assessed from public information. These never change the PFAS grade; a Likely flag caps the Verdict at “Buy with care.”
Plastic lid polymer identity and BPA/BPS status
Thermos does not publicly confirm the lid polymer type or state whether it contains BPA, BPS, or other bisphenols. Silicone is inherently safer than polycarbonate, but without material disclosure, residual risk cannot be ruled out.
Lid degradation and microplastic shedding from heat exposure
If hot liquids contact the plastic lid frequently, polymer can soften, cloud, or shed microscopic particles. This is a wear mechanism rather than a manufacturing defect, but users unaware of temperature limits may accelerate it.
Stainless steel corrosion and potential nickel leaching
Food-grade stainless steel (typically 18/8 or 304 grade) used in Thermos tumblers does not corrode or leach nickel under normal potable water or beverage use. Corrosion risk only arises if the tumbler is damaged or exposed to highly acidic or salty solutions for extended periods.
Silicone lid off-gassing or taste transfer
Silicone does not off-gas volatile organic compounds at room or moderate heat. Taste or odor residue is a cosmetic concern, not a toxicological one, and is reversible with cleaning.
Acetal or polycarbonate lock mechanism leaching
The slide lock mechanism does not contact beverages directly and is not submerged; leaching risk is negligible even if polymer is polycarbonate. Breakage of the lock is a functional failure, not a safety hazard.
What we don’t know
This grade is a model-based estimate from public materials, coatings, and brand disclosure at 72% confidence. It is not a lab result.
No independent PFAS lab test is on record for this exact product. A lab test could move the score in either direction.
The brand has not made a specific, verifiable PFAS-free statement, so part of this score reflects that missing disclosure rather than a confirmed material.
Formulations and coatings change between production runs. Always check the current label before buying.
More insulated drinkware tumblers grades
How we score: every product runs through the same public 0–100 rubric based on materials, coatings, brand disclosure, lab findings, and recalls. See the full methodology → Spotted a mistake? Report an error.