Silicone O-rings (VMQ) — properties, limits and applications

Silicone rubber (VMQ, trade names Silastic and Elastosil, older designation MVQ) is easy to spot on a warehouse shelf: naturally translucent with a reddish tinge and noticeably softer to the touch than the usual black nitrile. In practice you will meet it mostly on food-processing lines, in medical devices and anywhere the temperature swings from deep frost to hot air. A continuous range of -60 °C to +200 °C means that, together with fluorosilicone, it reaches deeper into the cold than any other common elastomer — and that temperature range is the main reason to buy VMQ. At the same time it is a material with sharply drawn weaknesses: poor mechanical strength rules it out of dynamic seals, and most petroleum-based media disqualify it chemically. This guide sums up when silicone makes sense and when to reach for another material.

The -60 °C to +200 °C temperature range: the headline strength

The continuous service temperature of VMQ runs from -60 °C to +200 °C, with short-term peaks up to +230 °C. For comparison: standard NBR works from -30 °C to +100 °C, EPDM from -40 °C to +130 °C, and FKM does handle the same +200 °C but stops at -20 °C on the low end. Silicone is the only sensibly priced elastomer that covers both extremes at once — frozen food and hot-air sterilisation sealed by the same compound. That makes it the first choice for high-temperature static applications and for low-temperature plants where other rubbers stiffen and lose their elasticity.

One important caveat: the range applies to static sealing in dry heat or in air. Hot air and steam are not the same thing — high-pressure steam chemically degrades silicone and belongs on the list of media VMQ must avoid. So decide in this order: medium → temperature → pressure → motion. The temperature range is only the second question; the first is always what exactly you are sealing.

Food contact, medical use and certifications

Among the common elastomers, VMQ carries the strongest certification profile for contact with food and the human body: FDA, USP Class VI, the German BfR, the European EC 1935/2004 regulation and the 3-A sanitary standard. The material is biocompatible and tolerates most foods, which is why it dominates food and dairy plants, medical devices and cosmetics production. A practical bonus: silicone is routinely supplied translucent, white, red, blue, green and black, so in food production you can easily colour-code seals by zone or medium — something the mostly black industrial elastomers cannot offer.

Chemical resistance: what silicone tolerates and what it does not

Silicone stands up very well to air, ozone and UV radiation, water, polar solvents and dilute acids — a dependable choice for outdoor static seals and for plants with regular wash-downs. The list of forbidden media, however, is long and painful in mechanical practice: most hydrocarbon oils, fuels, concentrated acids, alkalis and high-pressure steam. A silicone O-ring in mineral oil swells and loses its sealing ability; for oil duty the first choice remains NBR, and FKM at higher temperatures. Verify the specific material–medium pair in our chemical compatibility chart before you order.

Weak points: abrasion, tearing and dynamic duty

Silicone's biggest weakness is mechanical. VMQ has low abrasion resistance and tears easily — a nibbled or torn edge after installation over a sharp groove edge is a common sight with silicone. For dynamic seals, where the O-ring surface moves against the mating part — pistons, rods, rotating shafts with radial shaft seals — silicone is not a sensible pick; its home ground is static sealing: covers, flanges, housings. During assembly round off the edges, use an installation cone and never stretch the ring more than necessary.

VMQ hardness spans 30 to 80 Shore A — the bottom of that scale is far softer than anything NBR or FKM offers. Soft compounds seal at minimal clamping force, which pays off with fragile parts, plastic flanges and lids with little closing force. But the rule holds: the softer the compound, the more careful the installation and the less pressure the seal tolerates without the risk of extrusion into the gap.

On price, VMQ sits in the middle of the field. Against NBR (baseline 1.0) it comes out at roughly 3.5 times — noticeably cheaper than FKM at about 5 times and far cheaper than fluorosilicone FVMQ at around 10 times. You are not paying fluoroelastomer money for the food certifications and the extreme temperature range.

VMQ vs EPDM vs FVMQ: which one when

VMQ vs EPDM: for water, steam and outdoor applications up to +130 °C, EPDM is the cheaper (index 1.2) and mechanically tougher choice — with WRAS, KTW, DVGW and NSF 61 approvals for drinking water and a peroxide-cured grade for steam. Pick silicone when the temperature exceeds what EPDM can do, when you need cold down to -60 °C, or when the application demands biocompatibility and the full food-contact certification package of FDA / EC 1935/2004.

VMQ vs FVMQ: fluorosilicone keeps silicone's temperature range (-60 °C to +200 °C) and additionally resists fuels, aromatic hydrocarbons and chlorinated solvents. It is, however, a niche material for aerospace, military and low-temperature fuel systems, priced at around 10 times NBR. In everyday industrial practice reach for it only when you need to seal fuel below -20 °C, where standard FKM gives up.

Frequently asked questions

Will a silicone O-ring survive oil or fuel?

No. Most hydrocarbon oils and fuels are media that chemically attack silicone and cause swelling. For mineral oils up to +100 °C choose NBR, for hot oils up to +200 °C choose FKM. If you need fuel combined with extreme cold, the only silicone-family route is FVMQ.

Can I use a silicone seal in steam?

Water yes, high-pressure steam no — silicone will not tolerate it long-term. For steam duty the standard is peroxide-cured EPDM; keep silicone for dry heat and hot air up to +200 °C.

Why is a silicone O-ring translucent or reddish?

The natural form of a silicone compound is translucent with a reddish tinge — no carbon black, which is what colours common industrial elastomers black. Pigmented variants (white, red, blue, green and black) share the same base; the colour is there for identification on the line, not a mark of quality or resistance.

If you are unsure about the choice, start self-serve: the configurator suggests a suitable material and stock availability from your dimensions and medium, the chemical compatibility chart verifies the specific medium, the size converter finds the standard behind a measured ring, and the failure analysis guide helps when a seal keeps dying. If it is still unclear after that — typically when a food certification meets an unusual medium — write to Filip and he will walk through it with you.