Mountainsmith · Waterproof Outdoor Gear Storage Bags
Mountainsmith Zerk 40 Backpack
Unknown water-repellent coating treatment. High-performance packs often use PFAS-based coatings.
Mountainsmith doesn't disclose water-repellent coating chemistry. Outdoor backpacks typically use Teflon-family coating water repellents that often contain PFAS, and no third-party testing is available.
Still want this one anyway? Check the price on Amazon. We’d swap it.
Material
Nylon pack fabric with water-repellent coating
Brand disclosure
Brand is silent on PFAS
Lab data
No public lab test
What Mountainsmith Zerk 40 Backpack is made of, ingredients and materials
The Zerk 40 uses nylon pack fabric, a petroleum-derived synthetic polymer that is chemically stable and does not leach plasticizers or BPA under normal use. The critical unknown is the water-repellent coating (water-repellent coating) finish applied to the exterior. High-performance outdoor packs typically use either fluorocarbon-based (PFAS-containing) or newer polyurethane-based water-resistant coatings. Mountainsmith has not disclosed which chemistry they use, leaving the PFAS exposure profile unclear.
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.
Waterproof / stain-resistant treatment
Water-repellent coating treatments have historically used PFAS.
water-repellent coating (water-repellent coating) coating composition
Water-repellent coating finish is likely present but unconfirmed as PFAS or PFAS-free. Nylon base fabric itself is inert; risk is localized to coating only and not elevated during normal wear, but potential concern if coating degrades and particles are shed or if coating is abraded in manufacture or disposal.
What’s reassuring
Nylon polymer degradation and microfiber shedding
Nylon packs do not leach harmful monomers or plasticizers under typical hiking conditions. Microscopic fiber shedding during washing is documented for many synthetics but poses no acute toxicity risk to user; environmental impact is separate from consumer safety.
Dyes and colorants in fabric
No azo dyes, formaldehyde finishes, or heavy metal pigment contaminants are established issues in Mountainsmith packs. Nylon dyeing typically uses reactive or acid dyes with low toxicity if sourcing is conventional.
Seam tape and adhesives
Backpack seams may use polyurethane-based or solvent-adhesive taping; these are chemically stable in finished form and do not present known off-gassing or leaching hazards during normal use.
Zipper hardware (metal or plastic sliders)
Metal zippers on outdoor packs are typically nickel-plated brass or aluminum; no recalls or complaints of nickel leaching are on record for Mountainsmith packs. Contact dermatitis risk is negligible for non-sensitized users.
The full breakdown
The brand's record and disclosure
Mountainsmith is a mid-tier outdoor gear brand with no publicly available transparency reports on PFAS use, PFOA phase-out timelines, or chemical testing. The company has not faced documented product recalls or safety investigations specific to coating safety. Absence of disclosure is not reassurance; it reflects industry-wide opacity on water-repellent coating chemistry among most non-premium brands.
How it compares in its category
Nylon backpack construction is standard across the category and poses minimal chemical risk beyond the water-repellent coating. Premium brands like Patagonia, Arc'teryx, and some Gregory models now use PFAS-free water-resistant treatments or transparent labeling. Mountainsmith's silence on this point suggests either unphased PFAS formulations or cost-driven sourcing without environmental screening, typical of the mid-market segment.
If you buy it
Do not machine wash; hand rinse only with cool water to minimize coating degradation and any potential leaching of water-repellent coating residues. Avoid prolonged contact with harsh detergents or high heat (dryer or direct sun). The pack's lifespan is typically 5-10 years with normal hiking use; replace when seams fail or waterproofing visibly degrades. If PFAS-free certification matters to you, contact Mountainsmith directly for coating composition before purchase.
What we don’t know
- Basis
- Model estimate, 45% confidence, not a lab result
- Lab test
- None on record for this exact product
- Brand statement
- Mountainsmith has made none
Formulations change between production runs, so check the current label. How we grade.
Better-graded alternatives in Waterproof Outdoor Gear Storage Bags
REI Co-op
Trailgate Gear Bin Green 140 L
- Polypropylene storage bin, no water-resistant coating mentioned
- UV degradation and additive leaching
3 hazards checked on this product. See all of them.
Marmot
Tool Box
- Nylon, polyester, cotton blend; details unspecified
- Volatile organic compounds (VOCs) from polyester and nylon manufacturing
5 hazards checked on this product. See all of them.
Patagonia
Disperser Roll Top Pack 40L
- Recycled polyester with water-repellent coating (water-repellent coating) finish
- The brand calls it PFAS-free, which we have not verified
- PFAS
4 hazards checked on this product. See all of them.
More waterproof outdoor gear storage bags 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.