Thermos · Insulated Drinkware Tumblers
Stainless King Tumbler
Lower concern. Bare stainless steel has no PFAS risk.
Thermos Stainless King uses uncoated stainless steel as primary contact surface, which is inherently PFAS-free. Plastic lid and exterior components are standard concern but not high-risk application.
Shop Thermos on Amazon →Material
Stainless steel interior, plastic exterior 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 Stainless King uses 18/8 stainless steel (304 grade) for the interior, which is food-contact safe and does not leach metals or degrade into beverages under normal use. The exterior is plastic, likely polypropylene or similar commodity plastic, chosen for insulation and durability. Stainless steel's corrosion resistance and inert surface mean it poses no chemical migration risk even with acidic or hot liquids. The plastic lid and any gaskets are the only components where polymer degradation or leachables could theoretically occur, though this is not established as a concern for this specific product line.
The brand's record and disclosure
Thermos is owned by Groupe SEB and does not publish detailed material safety certifications or third-party testing results for most drinkware lines on their consumer-facing websites. The brand has no known recalls or documented chemical contamination incidents for the Stainless King tumbler line. Thermos does not publicly disclose manufacturing standards or material certifications (e.g., BPA-free statements) for this product, which reflects a broader industry norm for insulated drinkware rather than a red flag specific to this brand.
How it compares in its category
Insulated tumblers with stainless steel interiors are among the lowest-risk beverage containers; the main alternative (glass-lined or ceramic-coated) carries minor lead-in-glaze risk if coatings degrade. Most competitors in this price range (Hydro Flask, S'well, YETI) use identical or near-identical stainless steel construction with plastic lids, so the Stainless King is materially equivalent. The primary differentiator is brand reputation for durability and lid seal integrity rather than safety profile.
If you buy it
Wash the lid and gasket by hand or on the top rack of a dishwasher to prevent seal degradation; avoid prolonged exposure to extreme temperatures or aggressive scrubbing of interior surfaces. Do not use in a microwave (metal interior risk) and inspect the lid seal annually for cracking or clouding, which can indicate polymer breakdown. Stainless steel itself is essentially maintenance-free; replace the lid if the gasket dries out or the seal loosens. For hot beverages above 160°F, allow brief cooling contact before sealing to reduce pressure-related gasket strain.
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 degradation and leaching
The plastic lid and silicone gasket can degrade over years of repeated thermal cycling and dishwashing. No specific leachates have been documented for this product, but older or damaged lids may shed microplastics or release unknown polymer additives into beverages.
Stainless steel interior corrosion (minimal risk)
304-grade stainless steel is highly resistant to corrosion from beverages and does not leach iron, nickel, or chromium under normal use. Risk is negligible unless the interior is severely scratched and then stored with corrosive liquids for extended periods.
BPA or other polymer additives in exterior/lid plastics
Thermos has not published material composition for the plastic exterior or lid, so BPA, BPS, or phthalate presence cannot be confirmed or ruled out from public sources. However, no recalls or complaints specific to this tumbler line have been recorded.
Gasket material safety (silicone or rubber)
Most Thermos tumblers use silicone or synthetic rubber gaskets, which are food-safe but can absorb odors and flavors over time. No leaching incidents are on record, but material composition is not disclosed by the brand.
Manufacturing residues or contaminants
Stainless steel can occasionally retain machining oils or mineral deposits from manufacturing. Rinsing thoroughly before first use mitigates this; no contamination incidents have been reported for this product line.
What we don’t know
This grade is a model-based estimate from public materials, coatings, and brand disclosure at 78% 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.