What Is CNAF Gasket?

Quick Answer

A CNAF gasket (compressed non-asbestos fiber) is a soft gasket made from aramid fibers, glass fibers, or mineral fibers bound with a synthetic rubber binder (NBR, SBR, or EPDM) and compressed into sheet form. CNAF is the modern replacement for compressed asbestos fiber (CAF) gaskets, which have been banned or restricted in most countries due to health hazards. CNAF gaskets are covered by ASME B16.21.

CNAF sheet gaskets are manufactured by mixing reinforcing fibers with rubber binder and mineral fillers, then calendering the compound into sheets under heat and pressure. The resulting material provides good compressibility, chemical resistance, and sealing performance for low-to-moderate pressure and temperature services.

CNAF Composition

Component	Typical Content	Function
Aramid fiber (Kevlar)	15-25%	Primary reinforcement, tensile strength
Glass fiber	5-15%	Additional reinforcement, temperature resistance
Mineral fiber	0-20%	Heat resistance, dimensional stability
Rubber binder (NBR/SBR)	20-30%	Binds fibers, provides flexibility and sealability
Mineral fillers	20-40%	Bulk, hardness control, cost reduction

Different manufacturers produce CNAF sheets with varying fiber-to-binder ratios, resulting in grades optimized for specific services. Higher aramid content increases strength and temperature resistance. Higher rubber content improves sealability but reduces maximum temperature.

Standard Thicknesses and Sizes

Thickness	Application
0.5 mm (1/32”)	Thin joints, minimal compression needed
1.5 mm (1/16”)	Standard industrial gaskets; preferred thickness
3.0 mm (1/8”)	Rougher flange faces, moderate imperfections
4.5 mm (3/16”)	Heavily corroded or warped flanges
6.0 mm (1/4”)	Maximum; only for severely damaged flange faces

CNAF sheets are typically sold in standard sizes (1000 x 1000 mm, 1500 x 1500 mm, or 1500 x 2000 mm) and cut to the required gasket dimensions. Full-face or ring-type gaskets can be cut from the same sheet using die cutters or water-jet cutting.

Pressure-Temperature Ratings

CNAF Grade	Max Temp	Max Pressure	Typical Application
General purpose (NBR binder)	150 degC (302 degF)	40 bar (580 psi)	Water, air, oil, mild chemicals
High-temperature (SBR/mineral)	250 degC (482 degF)	50 bar (725 psi)	Steam, hot oil, exhaust
Chemical-resistant (EPDM binder)	180 degC (356 degF)	30 bar (435 psi)	Dilute acids, alkalis, solvents
Oil-resistant (NBR, high rubber)	120 degC (248 degF)	40 bar (580 psi)	Petroleum products, lubricants

These ratings represent continuous service limits. Intermittent or short-term exposures at higher temperatures may be acceptable but reduce gasket life. For service above 250 degC, switch to flexible graphite or spiral wound gaskets.

CNAF vs Graphite vs PTFE

Property	CNAF	Graphite Sheet	PTFE
Max temperature	250 degC	550 degC	260 degC
Chemical resistance	Moderate	Good (except oxidizers)	Excellent
Creep resistance	Good	Good (with metal insert)	Poor
Cost	Low	Moderate	Moderate
Availability	Widely stocked	Widely stocked	Widely stocked
Best for	Utilities, general service	Steam, hydrocarbons	Corrosive chemicals

Pro Tip

CNAF gaskets are the lowest-cost option for utility services (water, compressed air, low-pressure steam). However, avoid using CNAF on critical hydrocarbon or sour gas services where spiral wound gaskets or Kammprofile gaskets are specified by the piping class. CNAF is prone to embrittlement and blowout if exposed to temperatures or pressures beyond its rated limits.

Install CNAF gaskets with stud bolts and apply bolt torque per the ASME bolt chart. Use the minimum thickness that will seal the joint; thinner gaskets resist creep and blowout better.

Read the full guide to gasket selection