Selecting a gasket material is a three-variable problem: the lowest of temperature, pressure, and chemical compatibility always governs, so a one-axis "max temperature" chart is misleading without the pressure axis attached [S2][S3].
The practical envelope runs from elastomers at 121°C / 4 bar (synthetic rubber) up through PTFE at 260°C / 20 bar, flexible graphite to 1000°C, and metallic spiral-wound and ring-joint constructions beyond 1000°C at full ASME B16.5 Class 600+ ratings [S2][S4].
Where elastomers stop and semi-metallics take over
Solid elastomer gaskets typically top out near +120°C to +135°C, with silicone and Viton (FKM) extending the elastomer window to +250–300°C; once you cross +500°C, rubber flexibility is lost and graphite, mica, ceramic, or spiral-wound/ring-joint metallic designs become the only realistic options [S3]. Compressed non-asbestos fibre (CNAF) bridges the gap with an average range of -100°C to +400°C, which is why it dominates mid-range chemical and steam service [S3].
Mica (vermiculite) gaskets exceed +1000°C for exhaust and reformer service, and flexible graphite runs from -240°C up to +1000°C in non-oxidised service, withstanding about 144 bar as a homogeneous sheet and 193 bar when bonded to a stainless tanged insert [S3][S4]. The insert is not optional in high-pressure work: it stops the graphite from extruding under bolt load.
Pressure ceilings by material family
Natural rubber is limited to roughly 7 bar, general-purpose nitrile/EPDM/butyl/neoprene/Viton/silicone rubbers to about 10 bar, PTFE to about 55 bar, and CNAF fibre to 50–100 bar [S4]. Above that, expanded PTFE reaches about 206 bar, compressed graphite with stainless tanged insert exceeds 193 bar, and spiral-wound SS/graphite pushes well past 250 bar at temperatures where soft gaskets have already failed [S2][S4].
The engineering tool box reference tables quantify this for hard gaskets: solid PTFE caps at 150 000 (°F × psi) = 5320 (°C × bar) on the combined P×T axis, compressed asbestos historically at 250 000, carbon steel at 1 600 000, and 304/316 stainless at 3 000 000, with SS/graphite spiral-wound at 250 000 and SS/ceramic spiral-wound stretching to 1900°F / 1038°C for hot-gas service [S2]. Use that P×T product, not the standalone pressure figure, when you are screening candidates.
Flange class sets the pressure-temperature envelope
The ASME B16.5 class system runs 150 / 300 / 400 / 600 / 900 / 1500 / 2500, and the higher the class the more metal in the flange and the higher the allowable working pressure at any given temperature, with PN (Pressure Nominal) in bar as the European counterpart under BS EN 1092 / BS 4504 [S4][S6]. A Class 150 gasket belongs in a Class 150 flange: mismatching the gasket class to the flange class is a common procurement error that produces blowouts well before the material's own P×T limit is reached.
Allowable working pressure falls as temperature climbs on the ASME B16.5 metric rating tables: a Class 150 carbon-steel flange holds about 19.6 bar at -29°C but only about 9.9 bar at 400°C, and stainless variants follow a similar curve shaped by the material group's allowable stress [S6]. Always read the pressure rating at your actual operating temperature, not the room-temperature value printed on the flange.
Failure modes that flip the decision
Three physical limits drive gasket failure before the headline temperature or pressure is ever reached: creep relaxation (the bolt load bleeds out as the gasket yields over hours), extrusion (soft material squeezes into the flange bore under high pressure), and chemical attack (a polymer that is fine at 200°C in air can dissolve in a hot organic solvent at 80°C) [S3][S4]. Rubber exposed to high heat shrinks, melts, and ignites; at low temperature it transitions to a glassy, brittle state and cracks under any joint movement [S3].
That is why minimum seating stress matters as much as maximum pressure: a soft PTFE sheet may rate 55 bar, but if the bolted joint cannot deliver enough compressive stress to keep it seated through a thermal cycle, the joint will weep well below that number [S4]. Stiffer materials (graphite with tanged insert, CNAF, spiral-wound) tolerate lower seating stress and survive thermal cycling better, which is what makes them the default for ASME Class 300+ hot service.
Quick selection map by service
Cold water and compressed air below 121°C and 10 bar: Nitrile or EPDM [S2]. Mid-range chemicals to 260°C and 20 bar: solid PTFE, or expanded PTFE (ePTFE) where you need compliance up to 206 bar [S2][S4]. Steam and hydrocarbons to 400°C: CNAF, 50–100 bar [S3][S4]. Hot oil, steam, and reformer feed to 650°C: flexible graphite, with stainless tanged insert above 100 bar [S3][S4]. Exhausts, burners, and reformer outlets to 1000°C+: mica, SS/ceramic spiral-wound, or ring-type joint (RTJ) on ASME Class 600+ flanges [S2][S3].
For cryogenic service down to -240°C, flexible graphite and PTFE remain elastomeric in feel; most rubbers harden and crack below their glass-transition point, so specify EPDM (down to about -40°C) or FKM (down to about -25°C) only inside their published low-temperature limits [S3].
Reference anchors and sourcing
Engineers building flange specifications alongside the gasket material need the complementary gasket geometry reference, including the full-face versus ring-type decision on flat-face flanges, because the same material on a flat face and on a raised face seats very differently. The detailed material temperature envelopes and standards mapping (ISO, UL94, FAR 25.853 for fire performance) are catalogued on RAM Gasket Solutions' operating temperature guide, with FKM/Viton, silicone, Buna, EPDM, PTFE, and GYLON grade-level limits [S3][S5].
For pressure-temperature envelopes and the ASME B16.5 metric tables by material group, Universal Gaskets' PT rating reference pairs flange class with material group; the Engineering ToolBox gasket characteristics table gives the comparative P×T product limits across synthetic rubbers, PTFE, carbon and stainless steel, and spiral-wound families [S2][S6]. A general material overview of gaskets, sealing principles, and joint design is available on the spec encyclopedia.
Two signals to track next: ASME B16.5 working-group updates on high-temperature creep relaxation factors for graphite gaskets, and the gradual phase-out of legacy compressed asbestos data sets from OEM datasheets as more countries tighten handling rules [S2].
For component-level specifications, see construction machinery and equipment, and lamps and light fittings.