How to Select Insulation Gasket Materials Based on Application Temperature

An insulation gasket does two jobs at once: it blocks electric current between two pipe ends and it holds the seal across a wide service temperature. The material, not the sheet thickness, decides whether a joint survives cryogenic cooldown, hot gas or a steam-out. Most of these grades are supplied as flange gaskets for flanged joints, and the eight materials below are compared by dielectric strength, compressive and tensile strength, water absorption and temperature range, so a specification can be written from numbers rather than from habit.

Insulation Gasket Material Data

The eight grades cover three families: glass-reinforced laminates (G-7, G-10, G-11), phenolic sheets (phenolic and CR-filled phenolic) and specialty sheets (RPTFE and the two Klingersil grades). Dielectric strength shows how much voltage a given thickness blocks, compressive and tensile strength show how much bolt load and handling the sheet takes, and water absorption matters because absorbed water raises conductivity.

Note: typical published values for each grade. Temperature figures in °C are reproduced as listed in the source data; confirm the batch data sheet before purchase.

Glass-Reinforced Laminates: G-7, G-10 and G-11

These three laminates carry glass reinforcement and cover the whole cryogenic span. Inside the joint they work as part of a complete insulation kit: sleeves and washers stop the bolts from contacting the pipe flanges, while the gasket breaks the path between the two faces.

• G-7, glass-fibre reinforced silicone resin: -196 to 232 °C, 350 V/mil dielectric strength, 40000 psi compressive and 25000 psi tensile strength, 0.07% water absorption. Its low thermal expansion keeps the seal stable through extreme temperature swings.
• G-10, epoxy-impregnated glass laminate: the strongest sheet in the group at 50000 psi compressive and 45000 psi tensile strength, 550 V/mil and 0.1% water absorption, but the upper limit is 138 °C.
• G-11, the higher-temperature variant of G-10: the same dielectric and compressive figures, a top temperature of 176 °C and a slightly lower tensile strength of 43000 psi.

Whichever grade is chosen, set the actual service temperature 10-20% below the listed value. That margin covers ageing, thermal cycling and hot spots at the bolt line, and it keeps insulation resistance stable over a long service life.

Phenolic Grades and Filled PTFE

Below 100 °C the phenolic family is enough; where chemicals and thermal span drive the design, filled PTFE is the alternative.

• Phenolic, one of the earliest synthetic resins: 500 V/mil, 25000 psi compressive and 20000 psi tensile strength, 1.6% water absorption, -54 to 104 °C. It turns brittle under sustained heat, so keep continuous service below 100 °C.
• CR-filled phenolic: identical electrical and mechanical figures, a narrower upper limit of 79 °C and the same 1.6% water absorption.
• RPTFE (Gylon 3500), restructured PTFE: the widest range in the list at -196 to 260 °C and the lowest water absorption at 0.01%. Its mechanical figures are the lowest of the eight (2300 psi compressive, 1450 psi tensile), so it is specified for chemical and thermal duty rather than for load carrying.

Klingersil Grades and Temperature-Driven Selection

The two Klingersil sheets sit apart from the laminates: higher water absorption, moderate strength and listed temperature bands at the hot end.

• Klingersil C4430: 254 V/mil, 7200 psi compressive, 2466 psi tensile, 3% water absorption, listed at 175 to 200 °C.
• Klingersil C4400: 550 V/mil with the same 7200 psi compressive strength and 3% absorption, 2176 psi tensile, listed at 200 to 400 °C.
• Cryogenic duty: G-7, G-10, G-11 and RPTFE all start at -196 °C; compare compressive strength at the actual bolt load before choosing between them.
• Wet or buried service: absorption separates the candidates sharply - 0.01% for RPTFE and 0.07% for G-7 against 1.6% for the phenolic grades and 3% for the Klingersil sheets.
• Electrical duty: dielectric strength in this group runs from 254 to 550 V/mil, so G-10, G-11 and Klingersil C4400 lead when the isolation rating drives the design.

Match the grade to the highest and lowest temperature the joint will actually see, not to the average line temperature, and the insulation will hold for the whole service life.

Frequently Asked Questions

Which insulation gasket material covers the widest temperature range?

RPTFE (Gylon 3500) at -196 to 260 °C. G-7 is second at -196 to 232 °C and carries far higher mechanical strength.

Why does G-10 stop at 138 °C?

The epoxy binder sets the upper limit, not the glass reinforcement. G-11 is the higher-temperature variant at 176 °C, with tensile strength falling from 45000 to 43000 psi.

How much derating should be applied to the listed temperature?

Set the service temperature 10-20% below the listed value so that ageing and thermal cycling never push the material past its limit.

Why does water absorption matter in an insulation gasket?

Absorbed water raises conductivity and lets insulation resistance drift. The spread here is wide: 0.01% for RPTFE and 0.07% for G-7, against 1.6% for the phenolic grades and 3% for Klingersil.

Can a phenolic gasket run continuously at 104 °C?

That is the listed upper limit, but phenolic turns brittle under sustained heat, so continuous service below 100 °C is the practical choice.