Thinx For All Period Underwear Size M - New Women | Color: Red/Brown
Skip until Thinx discloses waterproofing chemistry or certifies.
Thinx uses a patented water-resistant finish on period underwear but does not disclose the coating chemistry or claim PFAS-free status. Waterproofing textiles commonly involves PFAS; without transparency or third-party testing, risk cannot be ruled out.
The better-graded swap
Modibodi
Modibodi Basic Mid-Rise Brief Black
90/100 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
Cotton blend with proprietary water-resistant coating (unspecified)
Lab data
No public lab test
What Thinx For All Period Underwear Size M is made of, ingredients and materials
Thinx For All uses a cotton blend (exact fiber ratio not publicly specified) paired with a proprietary water-resistant coating whose chemical identity is not disclosed. The coating is the functional barrier that prevents leakage, but without transparency on its composition, you cannot verify whether it contains PFAS, other fluorinated compounds, silicones, or synthetic polymers. Cotton itself is a benign fiber; the hazard profile depends entirely on the coating formulation and any dyes used in the fabric.
What’s concerning
Waterproof / stain-resistant treatment
Water-repellent coating treatments have historically used PFAS.
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.
Proprietary water-resistant coating composition undisclosed
Thinx has not named the coating chemistry; public records and brand statements do not specify PFAS-free status, fluorine content, or alternative binder. This lack of disclosure is itself a documented concern raised by consumer advocates and independent testers.
Coating degradation and microplastic generation over time
Any polymeric or synthetic coating on textiles can degrade with washing and wear, potentially shedding microparticles. Because Thinx's coating material is unidentified, you cannot assess whether it is more or less prone to this, or what the shedding material would be.
Leaching of coating components into skin or menstrual fluid during use
Warm, wet, acidic conditions (menstrual fluid) may promote leaching of water-resistant coating binders or additives if the coating is not fully cross-linked or if the formulation includes mobile components. Without ingredient disclosure, this risk cannot be quantified.
What’s reassuring
Heavy metals
No recalls or safety alerts are on record for Thinx period underwear related to azo dye hazards or heavy metals in the red/brown colorant. Standard cotton-dye safety standards typically apply; however, absence of testing reports means lower-risk, not zero-risk.
Source, FDA ↗Contact dermatitis or sensitization from coating or dyes
No widespread complaints linking Thinx For All to allergic contact dermatitis are publicly documented. Individual sensitivity to unidentified coating chemistry or dyes remains possible, especially in skin-contact intimate wear.
The full breakdown
The brand's record and disclosure
Thinx has not published material safety data sheets, full ingredient disclosure, or independent certification for this product. The brand has faced public criticism over PFAS use in period underwear but has not responded with detailed waterproofing chemistry or third-party testing results. This silence is a material gap; many competitors (e.g., Knix, Dear Kate) now disclose PFAS-free status or use alternative coatings (polyurethane, beeswax, or other named chemistries). Thinx's non-response leaves you without evidence of safety.
How it compares in its category
Period underwear as a category carries inherent PFAS risk because water resistance typically demands fluorochemistry or synthetic coatings. Thinx's refusal to disclose puts it behind brands that have publicly committed to PFAS-free materials or transparent coating identification. Cotton-based construction is standard and lower-risk than synthetic-heavy blends; the differentiator is coating chemistry, where Thinx offers no reassurance. If waterproofing durability and ingredient transparency matter to you, other brands provide both.
If you buy it
Wash in cold water, gentle cycle, and air-dry; heat (dryer, hot wash) may degrade the proprietary coating faster. Inspect the gusset monthly for signs of wear, pilling, or water-resistance loss (leaking or pooling during use). Replace after 1-2 years or sooner if the coating fails visibly. Do not bleach or use fabric softener, both of which can compromise coatings. Store in a dry place; damp storage can promote mildew and coating breakdown.
What we don’t know
- Basis
- Model estimate, 35% confidence, not a lab result
- Lab test
- None on record for this exact product
- Brand statement
- Thinx has made a specific claim
Formulations change between production runs, so check the current label. How we grade.
Better-graded alternatives in Period Underwear
Ruby Love
Rubylove First Period Kit +teen Period Underwear
- organic cotton, waterproof backing layer
- A third party reports verifying it as PFAS-free
- Coating degradation and microparticle shedding
2 hazards checked on this product. See all of them.
Lunapads
3-Pack BOOST Brief
- organic cotton blend, water-resistant gusset
- The brand calls it PFAS-free, which we have not verified
- Microplastic shedding from water-resistant barrier
Aisle
Super Hipster
- Organic cotton, wood pulp fiber
- The brand calls it PFAS-free, which we have not verified
- Azo dyes and synthetic dyes
2 hazards checked on this product. See all of them.
More period underwear 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.