The standard nobody reads but everyone should
ISO 10993 is the international standard for biological evaluation of medical devices. It is the framework that tells manufacturers whether a material is safe for prolonged skin contact. When a watch strap claims "medical-grade silicone," the meaningful question is: tested against which parts of ISO 10993, and passed?
Most buyers will never read the standard itself — it is 20+ parts spanning hundreds of pages. But understanding three sub-standards (10993-5, 10993-10, 10993-23) is enough to separate real medical-grade from marketing language.
ISO 10993-5: cytotoxicity
The cell-level test. A sample of the material is exposed to living cells in vitro. If the cells die or stop reproducing, the material is cytotoxic — it kills tissue on contact. A passing strap means the silicone does nothing harmful to cells over the test period.
This is the first gate. A material that fails 10993-5 cannot reasonably claim medical-grade anything. Cheap silicone often fails this quietly — manufacturers do not publish failures, they just do not publish results. Always ask for the test certificate, not the marketing line.
ISO 10993-10: skin irritation
The skin contact test. The material is held against skin (or animal-model skin in some tests) for an extended period. Reactions are scored — redness, swelling, raised tissue. A passing material produces no measurable irritation across the test population.
This is the test that matters most for a watch strap. You wear the strap 8–16 hours a day in direct skin contact. Sweat, sunscreen, and natural skin oils accelerate any irritation potential. A material that passes 10993-10 has been validated for exactly the conditions a strap operates in. Our medical-grade silicone explainer goes deeper on what passes and what fails here.
ISO 10993-23: sensitization
The allergy test. Some materials do not cause immediate irritation but provoke delayed allergic response after repeated exposure. ISO 10993-23 (which replaced the older 10993-10 sensitization section) screens for that. Critical for an item you will wear 5,000+ hours over its lifetime.
If you have ever developed a sudden rash from a strap you wore for months without issue, you experienced sensitization. The material was probably fine on day one — the immune system catches up later. Materials that pass 10993-23 are validated against this delayed-response mechanism.
What "medical-grade" actually means
| Claim | What to ask for |
|---|---|
| "Medical-grade silicone" | ISO 10993-5, -10, and -23 test certificates from a recognized lab |
| "Skin-safe" | At minimum ISO 10993-10 certificate |
| "Hypoallergenic" | ISO 10993-23 certificate; without it, the claim is marketing |
| "Food-grade" | Different standard (FDA 21 CFR 177.2600 for silicone) — not equivalent to medical-grade |
"Food-grade" and "medical-grade" are not interchangeable. Food-grade silicone is validated for short food contact under specific conditions. Medical-grade is validated for prolonged skin contact and, in some sub-grades, implantation. A strap claiming food-grade is making a weaker claim than medical-grade.
Why this matters for watch buyers
A watch strap is the most prolonged skin-contact item most people own outside of clothing. More wear hours than a wedding ring. More skin coverage than a glasses bridge. Higher temperature and sweat exposure than either. The material standard should match the use case.
This is also why cheap straps often cause skin issues that fancier straps do not. The price difference between certified medical-grade silicone and uncertified silicone is meaningful at industrial volume. Brands that skip the certification can sell straps for €10. Brands that pay for it cannot.
How POPSTRAP tests
POPSTRAP Drop 01 is platinum-cured medical-grade silicone, tested against ISO 10993-5, -10, and -23 at an accredited European lab. Certificates are available on request — email the workshop. The material is the same family used in implantable medical devices, not the kitchenware-grade silicone found in budget straps.
This is what we mean when we say medical-grade. Not a marketing line. A specific set of test results from a specific lab against a specific standard. If a strap does not have the certificates, the claim does not hold.
See Drop 01 for the full color range. Worn quiet. Built loud. POPSTRAP is an independent French brand, not affiliated with Swatch or Audemars Piguet.