S'well Stainless Steel Bento Box Onyx
Lower concern. Stainless steel bento box with no known PFAS sources.
S'well's stainless steel bento box uses an uncoated metal construction with silicone seals, materials with lower PFAS concern. No brand disclosure on PFAS, but no problematic coatings identified.
We flunk more products than we pass. This one earned its grade. How we grade
Material
stainless steel, silicone seals
Lab data
No public lab test
What S'well Stainless Steel Bento Box Onyx is made of, ingredients and materials
S'well's stainless steel bento is constructed from food-grade stainless steel (typically 18/8 or 18/10 alloy), which is chemically inert and does not leach metals into food under normal use. Silicone seals provide water resistance and compartment separation without requiring PFAS-based coatings. Stainless steel's passivated surface resists corrosion and does not degrade into particulates with typical handling, making it materially stable over years of use.
What’s concerning
Category baseline
The starting point for this type of product, before anything specific to this product is counted.
No PFAS disclosure
No public statement from the brand about PFAS in this product.
Silicone seal degradation
Silicone seals degrade with age, heat cycles, and UV exposure. Compromised seals lose waterproofing and may allow food leakage or bacterial growth if used for hot or wet foods; replacement or repair is straightforward but requires user vigilance.
Bacterial or mold growth in seals
Silicone seals can trap moisture and food residue if not cleaned thoroughly, creating conditions for mold or bacterial colonization. This is a maintenance issue, not a manufacturing defect, and is easily avoided with prompt drying and regular cleaning of seal crevices.
What’s reassuring
Bare uncoated material
Recorded as a bare, uncoated material with no surface coating or treatment.
Stainless steel leaching (chromium/nickel)
Food-grade stainless steel 18/8 or 18/10 does not leach chromium or nickel into food under normal refrigeration or room-temperature storage. Acidic foods (citrus, vinegar) at high temperatures can theoretically increase leaching, but this is not reported as a concern for bento boxes used as intended (packed lunches, not prolonged hot food storage).
Microplastic or coating shedding
Stainless steel does not shed microplastics, and no non-stick or protective coatings are present on this model to degrade. The material is inherently stable and does not fragment or release particles into food.
Lead
Stainless steel and food-grade silicone do not contain lead or cadmium by composition. No paint, glaze, or decorative coating is noted on this bento, eliminating the risk vector for these metals common in ceramic or painted food containers.
Source, ATSDR ↗The full breakdown
The brand's record and disclosure
S'well has not published detailed material safety or third-party certifications for this bento box. The brand's PFAS stance remains unspecified in public communications, though the material choice (stainless steel and silicone) inherently avoids common PFAS sources in food containers. No product recalls or safety controversies specific to this bento have been documented in public records.
How it compares in its category
Stainless steel bento boxes are among the lower-concern options in food storage, avoiding plastic leaching hazards (BPA, phthalates, microplastics) common in plastic compartment containers. Ceramic or glazed-ceramic alternatives carry potential lead or cadmium risks in decorative coatings; glass alternatives are heavier and breakage-prone. S'well's design and price position it in the premium durability segment rather than budget plastic competitors.
If you buy it
Hand wash with mild soap and water; avoid extended high-heat dishwasher cycles that can degrade silicone seals over time. Inspect seals annually for cracking or hardening; replace if compromised to maintain compartment separation and waterproofing. Do not expose to extreme temperature shocks (e.g., freezer to direct heat), which can stress the seal bonds. Stainless steel is durable; the bento's lifespan is typically limited by seal degradation, not the steel itself.
What we don’t know
- Basis
- Model estimate, 82% confidence, not a lab result
- Lab test
- None on record for this exact product
- Brand statement
- S'well has made a specific claim
Formulations change between production runs, so check the current label. How we grade.
Better-graded alternatives in Lunch Boxes
Klean Kanteen
Double Wall Vacuum Insulated Stainless Steel Food Canister Container with Leak Proof Lid
- Stainless steel body, silicone gasket lid seal
- The brand calls it PFAS-free, which we have not verified
- Silicone gasket degradation
3 hazards checked on this product. See all of them.
More lunch boxes 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.