Silicone Materials: The 7-Point Quality Checklist I Use Before Approval

Who this checklist is for

If you are choosing a silicone material for production, you don't need another article explaining what silicone is. You need a verification process. I'm a quality manager at a silicone fabricator, and I review roughly 350 incoming material lots and finished-goods batches every year. In 2024 I rejected 11% of first deliveries. Not because suppliers are dishonest, but because nobody had agreed on what would be tested, how, and against which tolerance.

This is the checklist I use. It works for silicone oils, silicone dispersions, mold-making silicone, and molded flexible parts. Whether you're a buyer, an engineer, or a small-business owner sourcing silicone components, it will stop you approving something you'll regret later.

Seven checks. In this order.

1. Identify the exact product, not the product family

Silicone is not a spec. Neither is "silicone oil." Neither is "silicone dispersion."

Dow Corning silicone oil, for example, covers dozens of different fluids: thin, volatile grades for cleaners and heat transfer, high-viscosity grades for damping and release. Molykote silicone dispersions can look like fluids, but they are designed to dry into bonded films, so storage, application, and testing are entirely different from plain oil. Mold-making silicone is usually a two-part rubber, not something you treat like either of the previous two.

Before comparing prices, get an exact product name, product code, and datasheet revision. If a supplier can't put those on a quotation, move on.

2. Request the certificate of analysis before the P.O.

A certificate of analysis (CoA) is not an afterthought. It should be in your hand before the purchase order is issued. The CoA needs to name the lot number, manufacture date, expiry date, test methods, measured values, and relevant compliance statements, such as FDA 21 CFR 177.2600 or USP Class VI.

Looking back, I should have enforced this earlier with one of our first dispersion suppliers. At the time, we needed material quickly, and the sales rep said the certificate would come with the delivery. It didn't. The coating film failed, and we had no lot number to trace and no measured values to compare. That cost us time, not just money. Now every order states plainly: no CoA, no release.

3. Verify cure chemistry for any food or mouth contact

The word "food grade" is not a description; it's a documented claim. If the silicone part will touch food, skin, or a mouth, check the cure system and the compliance evidence before you worry about hardness or color.

• Platinum-catalyzed, addition-cured silicone is the usual starting point for high-purity, food-contact, and skin-contact parts.
• Peroxide-cured silicone can leave catalyst by-products. Some grades are fine after post-curing, but that must be verified, not assumed.
• Tin-catalyzed, condensation-cured silicone is common in mold-making silicone. It is designed as a tooling material, not as a finished food-contact product.

A silicone bong can be made with a proper food-contact silicone, but it can also be made with a material never intended for mouth contact. Nothing in the product name tells you which one you're holding. The certificate does.

4. Test viscosity, hardness, and dispersion stability yourself

The CoA is the supplier's evidence, not your verification. It describes the lot on the day it was tested in their lab. It doesn't account for a cold warehouse, an open drum, or a bad transfer pump. Run basic checks on each incoming lot.

For fluid products, measure viscosity with a rotational viscometer at the temperature stated on the datasheet. For dispersions, check solids content and look for settling; a dispersion that has separated needs remixing before you do anything else. For cured silicone rubber, measure durometer Shore A according to ASTM D2240. Hardness may seem cosmetic, but it changes sealing force, compression set, and friction.

I have mixed feelings about cost-saving proposals that rely on material changes. One spreadsheet showed that switching to a lower-viscosity silicone oil would cut 15% from material cost and speed up filling. The logic was clean. My gut said the pump seals were specified for the current viscosity. We trialed one drum on the actual line, and it leaked in under an hour. The trial cost a morning; the switch would have cost a month.

5. Test friction against the real mating surface

If you've searched for coefficient of friction polypropylene vs silicone, here is the quality manager's short answer: there is no reliable single number. Coefficient of friction belongs to a pair of materials, not to one material alone.

Silicone rubber is soft and generally grips. Polypropylene is harder, has lower surface energy, and usually slides more easily in dry contact. But load, speed, surface texture, humidity, coatings, and lubricants can shift the result more than the polymer choice does. Data from a supplier's datasheet—often measured against steel—can be misleading if your part will slide against textured polypropylene.

Ask for a friction test against your actual counterpart, using a method like ASTM D1894 with conditions that reflect your assembly. If the supplier doesn't know the pairing, treat the COF value as an estimate, not a design input.

6. Make one sample before you make ten thousand

Skipping the first article is the most expensive shortcut in silicone processing. This is especially true with mold-making silicone.

A test coupon can cure perfectly and look fine. On your actual master, contaminants such as sulfur from modeling clay or residues from latex gloves can poison a platinum-cured silicone and leave sticky, uncured spots. You will not find that in a material datasheet. You will find it only when you run the real process.

We learned this the hard way. A supplier said their mold-making silicone was equivalent to our approved product. It wasn't. Working time was shorter, the mold closed late, and the parts stuck. That quality issue cost us a $22,000 redo and delayed a launch by six weeks. Now every new material includes a first-article step before full volume.

7. Mark every container with receiving and use-by dates

Silicone doesn't spoil the way food does, but it does age. Dispersions settle, catalysts lose activity, fluids can absorb moisture, and uncured rubber slowly changes. Put a receiving date on every drum, pail, and carton. Use oldest stock first. If material sits longer than six months, retest before it goes into production.

Three mistakes that cause most silicone material failures

Bottom line, these three problems show up repeatedly in incoming inspection:

1. Testing the certificate instead of the material.
2. Treating "food safe" as a description rather than a documented claim.
3. Comparing coefficient of friction values measured under different conditions.

You don't need a full laboratory to use this checklist. You need clear requirements, a few basic instruments, and the discipline to test before you trust. I'd rather spend ten minutes explaining a requirement up front than deal with an avoidable rejection later. An informed customer asks better questions and makes faster decisions—and that's better for both sides.