Thermos · Insulated Drink Tumblers
Thermos Stainless King Travel Tumbler
No coating on record that links to PFAS concern.
Thermos Stainless King is stainless steel with vacuum insulation and minimal internal coating. The brand has no PFAS statement on record. Material as recorded is not linked to PFAS.
We flunk more products than we pass. This one earned its grade. How we grade
Material
Stainless steel exterior, vacuum-insulated, minimal internal coating
Brand disclosure
Brand is silent on PFAS
Lab data
No public lab test
What Thermos Stainless King Travel Tumbler is made of, ingredients and materials
The Thermos Stainless King uses food-grade 18/8 stainless steel for the outer wall and vacuum insulation layer, which does not leach metals under normal use conditions. The interior surface is typically bare stainless steel or a minimal polymer liner, avoiding ceramic glazes, enamel coatings, or thick Teflon-type coating layers that are common leaching vectors in other drinkware. Stainless steel's passivated surface is stable across normal beverage temperatures and acidic drinks, making it chemically inert for typical consumer use.
What’s concerning
No PFAS disclosure
No public statement from the brand about PFAS in this product.
Category baseline
The starting point for this type of product, before anything specific to this product is counted.
Silicone lid and gasket degradation
Silicone seals can accumulate mold, mildew, or bacterial biofilm if not dried thoroughly after washing, particularly in the undercuts and contact surfaces. This is a maintenance issue rather than a manufacturing defect, but poor seal hygiene can affect beverage safety over time.
Bacterial or biofilm growth in sealed cavity
The vacuum-sealed gap between inner and outer walls is not accessible for cleaning; if the seal fails due to impact or material fatigue, moisture can be trapped and encourage microbial growth. This risk increases with age and mechanical stress but does not affect the beverage itself unless the inner wall is compromised.
What’s reassuring
Bare uncoated material
Recorded as a bare, uncoated material with no surface coating or treatment.
Metal leaching from stainless steel
Passivated 18/8 stainless steel does not leach nickel, chromium, or iron at detectable levels under normal beverage use (room temperature to hot drinks, non-corrosive fluids). No leaching has been reported in independent testing of this product type.
Thermal burn risk from hot contents
The insulated design works as intended to retain heat, meaning the exterior remains cool even with boiling liquids inside. This is a safety feature, not a hazard; no thermal injury risk is elevated compared to uninsulated drinkware.
Polymer interior coating or liner leachables
The Stainless King tumbler uses bare stainless steel or minimal polymer lining; if a polymer is present, it is typically a food-grade epoxy or polyester that is inert under normal beverage conditions. Thermos does not disclose the specific interior coating composition, and no contamination reports are on record.
The full breakdown
The brand's record and disclosure
Thermos has not publicly released detailed PFAS testing data or comprehensive material safety declarations for this product line. The company maintains ISO 9001 manufacturing certification and complies with FDA food contact substance regulations, but does not market PFAS-free status explicitly. No safety recalls, contamination reports, or regulatory violations specific to the Stainless King tumbler are documented in public records.
How it compares in its category
Stainless steel tumblers are among the lowest-risk drinkware options; they avoid the glazing hazards of ceramic mugs and the coating degradation risks of non-stick or enamel cookware. Most competitors in the insulated tumbler market (Hydro Flask, S'well, Contigo) use similar stainless steel construction with comparable safety profiles. The main differentiator is lid and seal design; Thermos seals are silicone-based and not known to be problematic, though long-term seal degradation can allow bacterial biofilm growth if not cleaned regularly.
If you buy it
Hand-wash the interior and lid thoroughly after each use, especially if left full for extended periods, to prevent mold and bacterial buildup in the seal. Avoid prolonged contact with highly acidic beverages (pH below 3) for months at a time, as even stainless steel can show minor pitting under extreme conditions. Replace the silicone gasket if it becomes visibly worn, cracked, or develops persistent odor. The vacuum seal can degrade over years of use; if insulation performance drops noticeably, replacement is more practical than repair.
What we don’t know
- Basis
- Model estimate, 78% confidence, not a lab result
- Lab test
- None on record for this exact product
- Brand statement
- Thermos has made none
Formulations change between production runs, so check the current label. How we grade.
Better-graded alternatives in Insulated Drink Tumblers
Klean Kanteen
20oz TKWide with Café Cap, Tofu
- Stainless steel bottle, stainless steel cap
- The brand calls it PFAS-free, which we have not verified
- Powder-coat cap degradation over time
3 hazards checked on this product. See all of them.
Klean Kanteen
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- Stainless steel body, powder-coat finish
- The brand calls it PFAS-free, which we have not verified
- Powder-coat finish degradation
3 hazards checked on this product. See all of them.
Klean Kanteen
Insulated TKWide Cap
- Stainless steel bottle, plastic cap and silicone gasket
- The brand calls it PFAS-free, which we have not verified
- Silicone gasket degradation and leaching
3 hazards checked on this product. See all of them.
More insulated drink 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.