Is silicone steam proof?

Many engineers think silicone is “magic” and will survive any heat and steam. I know how painful it is when that belief ends in leaks and unplanned shutdown.

Silicone is not fully steam proof. It works in mild, low-pressure steam and short cycles, but in long-term, high-pressure steam it ages much faster than in dry heat and often fails early.

So I never treat silicone as a universal “steam rubber”. I always check pressure, temperature, cycle time, and media before I say yes.

What does “steam proof” really mean for silicone?

People often use the word “steam proof” as if a rubber can ignore wet heat forever. In real projects, this idea is dangerous and very expensive.

For silicone, “steam proof” only means it can survive defined steam conditions for an agreed time. It does not mean infinite life in any steam temperature, pressure, or chemical mix.

How I define “steam proof” in real projects

When a customer asks me “Is silicone steam proof¹?”, I always answer with a few simple questions:

• ✅ What is the maximum temperature²?
• ✅ What is the steam pressure³ and is it saturated or superheated?
• ✅ How many hours per day will the part see steam?
• ✅ Are there cleaning agents⁴, additives, or oil in the system?

If we do not define these points, “steam proof” is only a marketing word. I prefer clear numbers. For example:

• 121 °C saturated steam, 2 bar, 30 minutes per sterilization cycle⁵
• Up to 10 cycles per day
• Light detergent present during cleaning, then rinse

In this type of mild condition, a good food-grade silicone⁶ can work well in gaskets, door seals, and tubing. I still call this “steam capable”, not “steam proof”.

Typical failure modes of silicone in steam

Silicone behaves very differently in steam than in dry hot air⁷. When the conditions are too harsh, I often see:

• ⚠️ Surface chalking or whitening
• ⚠️ Loss of tensile strength⁸
• ⚠️ High compression set⁹ (seal stays flat after cooling)
• ⚠️ Fine cracks, especially at sharp corners

Here is a simple comparison from what I see in the field:

🛠️ So when I say “yes” to silicone in steam, I always connect that “yes” to a defined test window and lifetime expectation, not to the word “proof”.

How does silicone behave in steam compared with dry heat?

Many data sheets show silicone working up to +200 °C or even higher. This is true in dry heat, but steam tells a different story.

Silicone keeps flexibility and low-temperature performance in dry heat, but in pressurized steam it loses strength faster, shows higher compression set, and often needs a much lower maximum service temperature.

Silicone in dry heat: where it is very strong

Silicone has an outstanding dry-heat window. This is why I love it for:

• Oven door seals
• High-temperature lamp gaskets
• Automotive engine bay seals (dry zones)
• Electric cabinet gaskets

In dry air:

• ✅ Silicone keeps elasticity at high temperature
• ✅ Silicone keeps low-temperature flexibility down to around −50 °C (compound dependent)
• ✅ Compression set is stable when the compound is designed well

This makes silicone a perfect “temperature bridge¹⁰” material in many designs.

Silicone in steam and wet heat: what really changes

Steam wraps the rubber in hot moisture. Water molecules can move into the silicone network. Over time, this wet heat:

• Speeds up aging
• Changes hardness and elasticity
• Increases compression set
• Can attack certain fillers and additives

I normally use a much more conservative temperature window for silicone in wet heat than in dry heat. A simple view looks like this:

*Exact numbers depend on compound, hardness, and test data. I always ask for real steam-aging results for critical parts.

So when I look at a drawing that only says “silicone 70 ShA, 150 °C steam”, I become careful. I know this is close to the danger zone for many silicone compounds in real steam, especially if pressure is high or cycles are long.

✅ In many cases, EPDM¹¹ is a better choice for saturated steam¹² in the 120–150 °C range, especially in HVAC and industrial hot water lines.

When can I safely use silicone in steam applications?

I do not reject silicone in all steam projects. I only avoid blind trust. There are many cases where silicone is a smart and safe choice.

Silicone works well in low-pressure, low-to-medium temperature steam with short cycles, especially in food, beverage, and medical equipment where approvals and low-temperature flexibility are important.

Typical steam use cases where I choose silicone

I often recommend silicone when a project looks like this:

• 🥤 Food and beverage machines with short steam cleaning cycles¹³
• 🧴 CIP/SIP tubing and gaskets with documented FDA or EU food contact approval
• 🏥 Medical sterilization where parts see repeated 121 °C autoclave cycles
• ❄️ Systems that also work at very low temperature, where EPDM becomes too stiff

Some concrete examples:

• Coffee machine silicone tubes that see short bursts of steam and hot water
• Autoclave door gaskets at around 121 °C, with controlled cycle count
• Small valves and connectors in lab devices where low extractables are key

Here silicone gives a mix of:

• ✅ Wide temperature range (cold to hot)
• ✅ Good compression set at moderate temperatures
• ✅ Clean surface and good biocompatibility in special grades

Checklist I use before I say “yes” to silicone in steam

Before I approve silicone, I go through a simple checklist:

1. ✅ Steam temperature: preferably around 121–130 °C, not extreme
2. ✅ Steam pressure: low to moderate, no strong superheat
3. ✅ Cycle pattern: defined cycle time and total lifetime cycles
4. ✅ Chemistry: clear information on detergents, disinfectants, and additives
5. ✅ Regulations: clear need for FDA, USP, or similar food/medical approvals

If we cannot answer these points, I suggest a material test¹⁴. My factory can mold trial pieces and run simple steam-aging tests so we see real behavior before mass production.

Here is a simple table that I share with buyers:

🛠️ This way, silicone is used where it shines, not where it will fail.

When should I avoid silicone and choose EPDM or FKM instead?

Some customers want one universal material for all hot lines. I always explain that this is not realistic, especially when steam, oil, and chemicals mix.

I avoid silicone in high-pressure, long-term steam and in systems with oil or aggressive chemicals, and I usually switch to EPDM for pure steam or FKM for steam plus oil or solvents.

EPDM vs silicone in steam

For saturated steam and hot water without oil, EPDM is usually my first choice. Reasons:

• ✅ EPDM has better resistance to hot water and steam aging¹⁶ than silicone in many ranges
• ✅ EPDM often has lower compression set in wet heat at 120–150 °C
• ✅ EPDM cost is lower than silicone for the same part

So for:

• HVAC steam coils
• District heating flanges
• Boiler gaskets

I almost always suggest a steam-grade EPDM instead of silicone.

FKM vs silicone in mixed media

When the system carries:

• Steam
• Oil mist or liquid oil
• Solvents or fuels

EPDM fails because of oil. Silicone may also suffer. In such cases, a suitable FKM grade may be better:

• ✅ FKM has strong resistance to oils and fuels
• ✅ Some FKM grades are designed for hot water and steam
• ⚠️ Cost is higher, but lifetime can be longer in harsh media

A simple comparison looks like this:

So when I read a spec that says “silicone gasket, 150 °C steam and oil”, I know we must change the material. If not, failure is only a matter of time.

How do I specify silicone parts for light steam service?

Many purchasing drawings only say “silicone 60–70 Shore A”. This is not enough to protect the buyer or the supplier when steam is involved.

To specify silicone for steam, you should define temperature, pressure, cycle time, and approvals, and you should ask your supplier for tested compounds with clear compression-set and steam-aging data.

Information I like to see on a drawing

When you send me a drawing for silicone in light steam, I like to see:

• Working temperature range and peak
• Steam type (saturated, low-pressure, short cycle)
• Required hardness, for example 60 or 70 Shore A
• Number and length of steam cycles per day
• Total lifetime target (for example, 1 year, 5 years)
• Required approvals: FDA, EU, USP, etc.

A clear note can look like this:

Silicone, 70±5 Shore A, food grade, suitable for 121 °C saturated steam, 30 minutes per cycle, up to 3 cycles/day, FDA 21 CFR 177.2600 compliant.

This gives me enough room to select or design a compound, but it also sets clear expectations.

Example: vague vs clear specification

Here is a simple table that shows the difference:

✅ With this type of spec, both sides know what “steam capable” means in numbers.

As a manufacturer, I can then:

• Propose the right silicone compound
• Send material data sheets
• Mold sample parts
• Support you with test reports and certificates (for example EN 10204 2.2 or 3.1 if needed)

If you want to discuss a real project, you can email me at info@rubberandseal.com with your drawing and working conditions. My team at Julong Rubber focuses on custom rubber seals and hoses for HVAC, industrial, and food projects, so we can help you compare silicone, EPDM, and FKM for your specific steam line.

Conclusion

Silicone is not fully steam proof, but it works well in mild, well-controlled steam conditions. For harsher steam, EPDM or FKM often gives a safer and longer-lasting result.