Coros · Water-Resistant Smart Rings & Bands
Coros FKM Rubber Watch Band
Lower concern. Material as recorded is not linked to PFAS.
FKM (Viton) rubber elastomer is the material as recorded for this watch band. The brand has no PFAS statement on record.
The better-graded swap
Smart Ring With Heart Rate Blood Oxygen Sleep Monitoring & Sports Modes - Size 8 - Gold
85/100 safety
Same rubric that flunked this product. The swap earned Excellent.
Still want this one anyway? Check the price on Amazon. We’d swap it.
Material
FKM (Viton) rubber elastomer
Brand disclosure
Brand is silent on PFAS
Lab data
No public lab test
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What Coros FKM Rubber Watch Band is made of, ingredients and materials
Coros FKM (Fluoroelastomer, branded as Viton) is a synthetic rubber compound engineered for chemical resistance and thermal stability. Unlike silicone or PVC watch bands, FKM does not require plasticizers like phthalates or BPA to achieve flexibility, nor does it leach these compounds into skin contact. FKM is not a material linked to PFAS and shows no established fragmentation into microplastics under normal wearable conditions (no heat exposure beyond ~80C, no UV degradation pathway that fragments the polymer).
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.
Azo dyes (synthetic colorants)
If the Coros FKM band is dyed (e.g., black, colored variants), synthetic azo dyes may be used in finishing. No testing or complaint history for this product is public; risk is hypothetical and consistent with dyed elastomer norms.
What’s reassuring
Base material not linked to PFAS
The main material recorded for this product is not one associated with PFAS.
Formaldehyde / VOCs
FKM elastomers do not require formaldehyde-based curing resins in standard synthesis. No manufacturing pathway in FKM watch band production typically involves formaldehyde exposure to the end product.
Source, ATSDR ↗Lead
No recalls or test results report heavy metal pigment contamination in Coros watch bands. FKM manufacturers typically do not incorporate lead or cadmium pigments; organic and inorganic non-toxic pigments are standard.
Source, ATSDR ↗Antimony in polyester or synthetic blends
FKM is not a polyester and does not contain polyester fibers. Antimony catalyst residues are irrelevant to this elastomer class.
Microplastics
FKM elastomers are highly cross-linked and do not fragment into microplastics under normal wearable temperatures (up to ~80C skin contact). Mechanical wear (friction, flexing) does not generate visible shedding in FKM the way softer rubbers or degraded silicones might.
Source, EPA ↗The full breakdown
The brand's record and disclosure
Coros (a GPS sports watch manufacturer) has not published material safety data sheets or transparency reports for accessory materials. The brand does not market PFAS-free credentials or hold third-party elastomer certifications (e.g., ISO 1629 purity grades). However, no consumer complaints, recalls, or testing results alleging contamination of Coros watch bands are recorded in public safety databases. The lack of disclosure reflects typical small-accessory brand practice rather than a safety red flag.
How it compares in its category
FKM watch bands are considered premium in the wearable elastomer category, they resist sweat, UV, and thermal fluctuations better than silicone or rubber blends, and they carry no known phthalate or BPA risk. Silicone alternatives (common in budget sports watches) are not a material linked to phthalates but can shed microsilica particles if degraded. Polyurethane or PVC bands carry higher phthalate leaching risk under sweat and heat. FKM sits at the safety and durability high end.
If you buy it
Wash the band regularly with mild soap and water to remove sweat and salt buildup, which can accelerate minor surface wear but not material breakdown. Do not expose to temperatures above 100C or direct flame. Replace the band if visible cracking, hardening, or surface peeling develops (typically 2-5 years of daily wear); these are signs of age, not safety failure. FKM does not require special storage and resists mold and bacterial colonization better than organic rubber.
What we don’t know
- Basis
- Model estimate, 72% confidence, not a lab result
- Lab test
- None on record for this exact product
- Brand statement
- Coros has made none
Formulations change between production runs, so check the current label. How we grade.
More water-resistant smart rings & bands 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.