Silicone rubber (VMQ) is the workhorse elastomer across defense sealing, vibration isolation, and insulation, with usable service from -120°F to +450°F (-85°C to +230°C) per Eutsler Technical Products' 2026-08-05 datasheet [S1].
For fuel-system, weapons-platform, and ground-vehicle hardware, the real decision is which sub-family of silicone to specify, and where to step out of silicone into a fluorocarbon (FKM) or perfluoroelastomer (FFKM) instead, since defense elastomer choices are driven by chemistry, temperature, and shock profile rather than by generic "silicone is flexible" claims [S2].
VMQ Core Envelope and Why Defense Specs It
VMQ's Si-O-Si backbone gives -120°F to +450°F flexibility, ozone and UV resistance, high dielectric strength, low compression set after heat aging, and biocompatibility when FDA-grade compounds are used, per the Eutsler performance list dated 2026-08-05 [S1]. For general-purpose defense gaskets, hatch and door environmental seals, cable jackets, and lighting housings, this envelope is the cheapest path that still passes MIL-spec weathering.
AMS-grade silicones are engineered specifically for thermal cycling from -65°F to +500°F, dimensional stability under load, and low compression set, per Elastapro's 2026-05-01 guidance on aerospace and defense silicones [S3]. When the program calls out an AMS or MIL-PRF specification rather than a generic VMQ, hardness and tensile targets are baked into the standard, so the engineering work shifts from compound selection to lot traceability and cure-post-cure verification.
FVMQ, FKM, and FFKM: When Silicone Is Not Enough
Fluorosilicone (FVMQ) is the branch defense fuel-system seals default to, because it keeps the low-temperature flexibility of VMQ while resisting jet fuel, hydraulic fluid, and synthetic lubricants that swell standard silicones; Eutsler's 2026-08 datasheet positions FVMQ as especially valuable for aerospace, defense, and high-performance automotive systems requiring chemical stability across severe service [S1].
Where the chemistry is more aggressive than FVMQ can handle, defense molding houses step straight to FFKM per American Rubber Corp's 2026-07-28 defense page, which lists fluorosilicone for fuel-system sealing and FFKM for the most aggressive chemistries as matched-to-fluid choices, not optional upgrades [S2]. Calendered silicone sheet can be formulated across 10 Shore A to 90 Shore A and qualified to MIL-Specs, per Reiss Manufacturing's 2026-04-16 release, so the form factor (calendered stock, molded O-ring, or extruded profile) is independent of the spec callout [S6].
For a quick reference on how VMQ sits in the broader elastomer landscape, the industrial rubber overview covers the cross-family comparison, while the nitrile rubber (NBR) entry explains why NBR is the cheaper fuel-and-oil alternative that loses to FVMQ once low-temperature flexibility matters.
Hardness, Compression Set, and the Numbers That Matter
Defense sealing decisions live in narrow ranges. Shore A for soft gaskets, seals, and hoses typically runs 20 to 80, with Shore D 30 to 70 reserved for stiff structural parts, per the 2026-04-01 rubber and silicone specifications reference [S4]. Calendered defense silicones can be specified across 10 Shore A to 90 Shore A, which brackets the entire soft-seal window plus the firm-mount upper end [S6].
Compression set is the second gate: AMS-grade defense silicones are picked specifically for "low compression set" so a hatch seal or connector gasket keeps preload after years of thermal cycling, not weeks, per the 2026-05-01 Elastapro guidance [S3]. For static O-rings that are replaced at depot, this is a maintenance-cost issue; for dynamic seals on weapons-platform recoil systems, it is a mission-readiness issue, which is why American Rubber Corp lists recoil-system components in the same product family as static hatch seals [S2].
Process Form Factor: Molded, Extruded, LSR, and Rubber-to-Metal
Form factor changes the supplier list, not the material spec. Compression molding, transfer molding, and extrusion cover the bulk of VMQ defense parts, while liquid silicone rubber (LSR) injection molding opens complex geometries, insert overmolding onto plastics or metals, and tight-tolerance medical-style parts, per the 2026-03-26 medical LSR feature whose processing rules translate directly into cleanroom defense electronics [S5].
Rubber-to-metal bonded isolators, engine mounts, and bumpers are a separate supply chain because the bonding step is process-critical; American Rubber Corp runs these as a distinct product family under ISO 9001:2015 and IATF 16949:2016 with PPAP and first-article inspection on request [S2]. For non-bonded VMQ and EPDM weatherstrip on the same vehicle platform, the EPDM rubber entry explains the weather-and-ozone overlap that makes EPDM a frequent co-spec alongside silicone.
Comparison: VMQ vs FVMQ vs FKM/FFKM for Defense
For the most common decision on a defense program, three criteria do the sorting: low-temperature flexibility, fuel/hydraulic-fluid resistance, and upper temperature ceiling. Standard VMQ covers -120°F to +450°F with the best low-temperature flexibility but the weakest fuel resistance, so it is the default for hatch, door, access-panel, and NBC inflatable seals [S1][S2]. FVMQ holds most of that low-temperature range while adding jet-fuel and hydraulic-fluid resistance, which is why fuel-system O-rings default to FVMQ rather than VMQ [S1][S2]. FKM and FFKM step in when upper temperature and chemical resistance dominate and the low-temperature penalty is acceptable, with FFKM reserved for the most aggressive chemistries per American Rubber Corp's matched-to-fluid approach [S2].
The trade-off in one line: pick VMQ when only temperature and weather matter, pick FVMQ when fuel or hydraulic fluid is in the loop, pick FKM or FFKM when chemistry is the binding constraint and cold-flex is not. For applications where the elastomer is also doing electrical insulation at temperature, the silicone rubber encyclopedia entry summarizes the dielectric-strength and UV-resistance behavior that drives those callouts.
Limitations and Failure Modes Engineers Watch
Silicone's well-known weaknesses matter in defense service: poor tear strength, weak abrasion resistance, and high friction in dynamic unlubricated contact, which is why dynamic reciprocating seals in hydraulic actuators usually spec FKM or FFKM even when the rest of the platform is VMQ [S2]. Swelling and extraction in non-polar fuels force the switch to FVMQ, and at very high temperatures (>200°C continuous) VMQ compression set drifts unless the compound is post-cured and the AMS callout is enforced [S3].
For naval and amphibious programs, ASTM D1149, ASTM D413, and MIL-STD-810 exposure profiles add saltwater, fuel-oil, and thermal-shock requirements that change the compound choice, so a print should always list the fluid list, temperature cycle, and any MIL-STD profile before the elastomer is locked in, not after.
For adjacent silicone-spec work, the rail EN 45545-2 silicone selection map covers the fire-and-smoke side of the same polymer family, while the marine silicone selection map handles saltwater and UV service that overlaps with coastal defense hardware.
Two signals to track over the next quarter: AMS revisions tightening low-temperature compression-set limits on defense silicones, and defense-mold shop capacity for FVMQ and FFKM compounds, since matched-to-fluid capability is more often the schedule risk than the material data sheet itself [S2][S3].