Medical-Grade Liquid Silicone Rubber for Menstrual Cups: Hardness, Compliance and Sourcing
Menstrual cups leave little room for error: a 0.1 mm wall-thickness deviation, a two-point hardness drift or a batch with residual volatiles can end a brand's relationship with its moulder. The cup is folded, inserted, opened by suction and boiled between uses - so the material must be soft enough to fold, resilient enough to seal, transparent enough to inspect and clean enough to defend in an audit.
Quick answer
Specify a platinum-cured, addition-cure medical LSR in the 20–40 Shore A range with high tear strength and shrinkage your mould can absorb. For most cups, 20A (AS8320EA/B) or 30A (AS8330EA/B) gives the foldability and rim seal users expect, while 40A suits firmer cups and stems. Ask for ISO 10993 biocompatibility, FDA 21 CFR 177.2600 total extractives and REACH SVHC documentation, insist on post-cure, and check transparency batch by batch before moulding rather than after.
What a menstrual cup demands from the material
Foldability at 20–30 Shore A. A cup has to collapse to roughly a third of its diameter and spring back without permanent deformation. Above about 40A the fold becomes hard for first-time users; below 15A the rim will not hold suction.
Tear strength at the rim and air holes. Both are thin sections and stress concentrators. A cup rarely fails in tension - it tears at a hole, which is why tear strength matters more.
Transparency for inspection. Dyes and pigments hide foreign matter, flow lines and incomplete cure.
Low extractables and no odour. The product is boiled and used internally; volatiles show up as smell and failed extractive testing.
Colour options without reformulation. Many brands launch clear, then add a tinted variant; the base grade should accept masterbatch without a hardness shift.
Hardness selection: the AS8320–AS8370 range
ANYSIL's medical LSR series runs from 20A to 70A on the same base chemistry, so a brand can move between hardnesses without re-qualifying a different material. The values below are from the published datasheet for the menstrual cup LSR grade.
| Grade | Hardness (Shore A) | Density (g/cm³) | Tensile (MPa) | Elongation (%) | Tear (kN/m) | Linear shrinkage (%) |
|---|---|---|---|---|---|---|
| AS8320EA/B | 20 ± 2 | 1.05–1.11 | ≥ 6 | ≥ 600 | ≥ 20 | 1.8–2.2 |
| AS8330EA/B | 31 ± 2 | 1.05–1.11 | ≥ 7 | ≥ 600 | ≥ 25 | 1.8–2.2 |
| AS8340EA/B | 40 ± 2 | 1.10–1.12 | ≥ 8 | ≥ 550 | ≥ 25 | 1.8–2.2 |
| AS8350EA/B | 50 ± 2 | 1.12–1.14 | ≥ 9 | ≥ 450 | ≥ 30 | 1.8–2.2 |
| AS8360EA/B | 60 ± 2 | 1.13–1.15 | ≥ 9 | ≥ 350 | ≥ 35 | 1.8–2.2 |
| AS8370EA/B | 70 ± 2 | 1.13–1.15 | ≥ 9 | ≥ 300 | ≥ 35 | 1.8–2.2 |
Three readings matter when specifying. Elongation falls faster than tensile rises: going from 20A to 40A keeps tensile at 8 MPa or better but drops elongation from 600% to 550%, and by 70A it is 300%. Tear climbs with hardness, which is why firm cups resist rim damage better and why a 20A grade needs careful mould design at the air holes - 20 kN/m is respectable but it is protecting a very thin section. And linear shrinkage is held at 1.8–2.2% across the whole range, unusually narrow for LSR, which is what lets a moulder avoid re-cutting steel when a brand changes hardness. Cut the tool for the midpoint and validate with a first-article inspection at production cure temperature, not on a lab press.
Transparency is a quality-control decision
LSR is naturally clear, and raw-material clarity is one of the few quality indicators you can check without a lab. Cloudiness in the drum, a yellow cast or visible gel particles indicate moisture uptake, contamination or partial cure - so keep a retained sample per batch and compare it under the same lighting.
For the finished cup, inspection lighting matters as much as material clarity. A translucent cup backlit at 45° reveals flow lines, knit lines at the stem junction and voids that a top-lit bench will miss - so ask your moulder what inspection setup is used.
The compliance stack to request
For a body-contact, boil-sterilised product, one certificate is never enough. The package behind the medical LSR range should include ISO 10993 biocompatibility testing relevant to mucosal contact (cytotoxicity, sensitisation, irritation as the minimum set); FDA 21 CFR 177.2600 total extractive residues, the standard extractables test for rubber in repeated food contact and a widely accepted leachables proxy; a REACH SVHC declaration for the batch; RoHS and phthalate-free statements; ISO 9001 at the plant, which is what makes batch traceability credible; and a TDS and SDS for the specific grade, not a generic silicone document.
ANYSIL holds ISO 9001, FDA, LFGB, REACH, RoHS and SVHC documentation plus medical biocompatibility testing for its medical grades; current certificates are listed on the certificate page and can be issued against your batch number. Destination rules stay with your regulatory team - EU buyers often add LFGB or BfR recommendations, some US channels ask for USP Class VI, and Chinese domestic sales require GB 4806. Raise these at quotation stage, not after the PO.
Post-cure: the step that decides whether your cup smells
The datasheet specifies post-cure at 200 °C for 4 hours for parts that contact food, and the same logic applies to any body-contact cup: post-cure drives off residual low-molecular-weight volatiles, stabilises hardness and removes the "new rubber" odour consumers notice at the first boil.
Two practical points: post-cure shrinks and slightly hardens the part, so it must precede final dimensional approval, and it must be temperature-verified - a 25 °C swing at the oven door produces hardness variation that surfaces only in a compression-set test.
Processing notes
The A and B components are mixed 1:1 and fed into the injection unit; they must stay separate until use, because mixed material begins to cure and cannot be recovered. Watch three controls: metering accuracy (a 2% drift in A:B ratio moves hardness and cure speed - calibrate the dosing pump weekly), mould temperature uniformity (cavity-to-cavity variation above 5 °C creates hardness variation no incoming inspection can fix), and degassing, since micro-voids read as white specks in a clear cup.
Packaging, shelf life and first orders
Material ships in 20 kg pails or 200 kg drums with a PE liner; shelf life is one year in closed containers in a cool room. Plan quantities against a realistic 6–9 month run rather than a 12-month forecast, and check that the liner is intact on arrival - a punctured liner in a humid climate turns a good batch into a cloudiness claim. A 20 kg pail is enough for a mould trial and a small pre-production run.
What drives price between suppliers
Quotes for the same 20A medical LSR can differ by 30% or more: base polymer quality (fumed versus precipitated filler and the resulting tear strength), whether the grade is genuinely platinum-cured, the certification package, who performs post-cure, and packaging. Compare on tear strength and elongation at your target hardness.
RFQ checklist
Include application (cup, disc, stem, case), target hardness with tolerance, transparency or colour, tear and elongation minima, annual and first-order volume, cavity count and press type, available cure temperature, post-cure responsibility, certification list with standard numbers, destination market, packaging and required lead time.
FAQ
Which hardness is best for a menstrual cup? Most cups sit at 20–30 Shore A: soft enough to fold and insert, firm enough for the rim to open and seal. 40A is used for firmer cups and stems; 50A and above is generally too stiff for the cup body but suits applicators and cases.
Is menstrual cup silicone the same as food-grade silicone? Medical LSR is specified to stricter biocompatibility standards, but many grades are tested against both. ANYSIL's cup grade is ISO 10993 certified, passes FDA 21 CFR 177.2600 total extractive residues, is SVHC REACH tested and also meets food-grade requirements - which is why the same series is used for nipples and kitchenware.
Why does my cup have a rubber smell after moulding? Almost always incomplete post-cure. Volatiles from the curing reaction stay in the part until driven off at elevated temperature. A verified 200 °C / 4 h post-cure with even airflow removes the smell; longer in-mould cure does not.
What is the minimum order for a first trial? A 20 kg pail normally covers a mould trial plus a small pre-production run - the sensible way to qualify a grade before drums. Samples ship freight collect.
Get a grade recommendation and a sample pail
Send your cup design (wall thickness, rim geometry, stem), target hardness and destination market, and we will recommend a grade from the AS8320–AS8370 series, share the matching TDS, SDS and test reports, and arrange a free sample for your mould trial. ANYSIL produces medical and food-grade LSR in Guangzhou with 3,600+ tonnes of annual capacity and exports to more than 50 countries. Start from the menstrual cup LSR page or send your specification through the inquiry form.