Flex · Menstrual Cups
Silicone Menstrual Cups
Lower-concern product; silicone cups don't require PFAS-prone treatments, but manufacturer silence on sourcing limits full confidence.
Flex menstrual cups are made from silicone, a non-fluorinated polymer with no inherent PFAS risk for the product itself. Menstrual cups lack the features that typically drive PFAS use (nonstick coatings, water repellency, stain resistance).
Shop Flex on Amazon →Material
Medical-grade silicone (body-contact surface)
Brand disclosure
Brand is silent on PFAS
Lab data
No public lab test
Why this grade
Category baseline
period care is a category where PFAS exposure is more common.
No PFAS disclosure
No public statement about PFAS in this product.
Safe base material
Made from a material with no inherent PFAS use (ceramic, mineral, or natural fiber).
The full breakdown
What it's made of and why it matters
Flex menstrual cups use medical-grade silicone, a synthetic rubber polymer that does not contain BPA, phthalates, or latex. Medical-grade silicone is selected for this category specifically because it resists degradation in warm, acidic environments (vaginal pH 3.8-4.5) and withstands repeated boiling sterilization without leaching. Unlike lower-grade silicone or rubber products, medical-grade formulations are cross-linked to minimize monomer migration.
The brand's record and disclosure
Flex has marketed its cups as FDA-cleared (as a Class II medical device) and does not publicly disclose PFAS testing or sourcing transparency. The company's website emphasizes safety certifications but does not address per- and polyfluoroalkyl substance (PFAS) content or manufacturing controls. No recalls, contamination incidents, or health complaints are documented in FDA databases or independent safety databases for Flex menstrual cups.
How it compares in its category
Medical-grade silicone cups (Flex, Diva Cup, Saalt, etc.) are chemically the safest menstrual product option; they avoid the bacterial growth and absorbency concerns of tampons and pads, and silicone is more chemically inert than thermoplastic elastomers or lower-grade rubbers. Flex's FDA device classification and multi-year market presence without reported adverse events place it in the established, lower-risk tier of this category.
If you buy it
Boil or use a dedicated silicone cup sterilizer between cycles; do not expose to extreme heat (e.g., dishwasher high heat or direct flame), which can degrade the surface over time. Replace every 2 years or if you notice discoloration, roughness, or persistent odor that cleaning does not remove. Store in a breathable cotton pouch, not airtight plastic, to prevent bacterial or mold growth.
Beyond PFAS: other things we checked
Established hazard classes for this product type, assessed from public information. These never change the PFAS grade; a Likely flag caps the Verdict at “Buy with care.”
Silicone monomer leaching (oligomers and low-molecular-weight polymers)
Medical-grade silicone used in Flex cups is cross-linked to minimize monomer release. No documented cases of cyclic or linear oligomer contamination in clinical use of medical-grade menstrual cups; heating to sterilization temperatures (100°C boiling) does not mobilize residual monomers at measurable levels in published silicone biocompatibility literature.
Bacterial or fungal biofilm growth on cup surface
If cups are stored wet or in airtight containers, or not fully dried after cleaning, silicone's smooth surface can accumulate biofilm. This is not a manufacturing defect but a user-maintenance issue; proper boiling and air-drying eliminate risk.
Allergic contact dermatitis or irritation from silicone additives or residual processing c
Medical-grade silicone formulations are tested for skin irritation and sensitization under ISO 10993. No publicly reported cases of contact dermatitis from Flex cups; silicone allergies are rare, and FDA clearance implies skin compatibility testing.
Surface degradation or discoloration over extended use
User reports document yellowing or slight surface roughening after 2-3 years of use, typically linked to heat exposure, soap residue buildup, or mineral deposits from tap water. This is cosmetic and does not indicate chemical breakdown into the vaginal tract; replacement is recommended for hygiene and user confidence.
PFAS in raw silicone material or manufacturing solvents (no disclosure)
Flex does not publicly disclose PFAS testing or supplier audits. Medical-grade silicone itself does not require PFAS-coated manufacturing (unlike non-stick cookware), but fluorinated solvents may be used in polymerization. Manufacturer silence prevents full confidence, but silicone chemistry does not inherently drive PFAS risk as high as other consumer goods.
What we don’t know
This grade is a model-based estimate from public materials, coatings, and brand disclosure at 72% confidence. It is not a lab result.
No independent PFAS lab test is on record for this exact product. A lab test could move the score in either direction.
The brand has not made a specific, verifiable PFAS-free statement, so part of this score reflects that missing disclosure rather than a confirmed material.
Formulations and coatings change between production runs. Always check the current label before buying.
Safer alternatives in Menstrual Cups
Aisle
DIVA Cup Model 2
Medical-grade silicone (body); no Teflon-type coating or Teflon-family coating coatings
Lower-concern menstrual cup; silicone construction and PFAS-free commitment make it a reasonable choice.
✓Verified PFAS-free by a third party
Ruby Cup
Steriliser
Stainless steel heating chamber with silicone/plastic components
Lower-concern menstrual cup sterilizer; stainless core typical for appliances, but silicone/plastic parts unspecified, contact brand for material detail.
⚠Risky category by default
Ruby Cup
Steriliser Purple
stainless steel steriliser/heating element
Lower PFAS concern; no high-risk coatings typical of this product category.
⚠Risky category by default
More menstrual cups 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.