Virgin PTFE carries a published service window of -200 to +260 °C, a density band of 2.1-2.2 g/cm³, and a mould-shrinkage range of 3.1-7.7% at a 330-380 °C moulding temperature, per standard polymer datasheet data [S1].
For defense and aerospace sealing, those four numbers gate every grade decision: continuous thermal range, specific gravity, shrinkage tolerance, and processability are the variables a buyer can screen on before opening a part drawing [S1].
Virgin vs filled PTFE: where each grade earns its place
Virgin PTFE is the only grade that retains the polymer's full chemical resistance and the lowest coefficient of friction of any commercial plastic, so it stays the default for any seal or gasket that touches aggressive media [S1]. Its 3.1-7.7% mould-shrinkage band, however, forces tight tool compensation and rules it out for tight-tolerance dynamic lips on hydraulic actuators [S1].
Filled PTFE compounds (glass, carbon, bronze, graphite, MoS₂, and PEEK blends) trade chemical inertness for hardness, creep resistance, and thermal conductivity; in defense hardware they are the grades specified where extrusion under system pressure would otherwise wipe a virgin lip in hours. The same material family is used in spring-energized seal jackets, where the polymer is precision-machined and bonded to a metal energizer that holds even contact load across the sealing surface [S2]. Bal Seal Engineering, which supplies springs and seals into military aerospace, lists PTFE among its precision-machined jacket materials and pairs it with custom alloy springs for rotary, reciprocating, oscillating, and static service [S2].
Spring-energized seals and canted-coil contacts: the two defense workhorses
Spring-energized PTFE seals are machined from premium polymers and use a spring energizer to hold the lip against the hardware across pressure swings, with jacket materials customized to the required temperature, pressure, speed, and chemical envelope [S2]. For procurement, the three engineering claims to verify on the supplier's datasheet are controllable friction, media/temperature resistance, and wear-regulating spring load [S2].
Canted-coil springs are a separate product line from the same supplier family, and the published functional spec is mechanical fastening plus electrical conduction plus EMI/RFI shielding in a single component, with multiple independent coil contact points carrying current under shock and vibration [S2]. For defense avionics, that 3-in-1 function (fasten, conduct, shield) directly addresses the size, weight, and power, or SWaP, budget that drives modern platform redesigns, and the same supplier cites heritage from Apollo-era tooling through Mars-class mechanisms to current avionics assemblies [S2]. This is the practical pattern: PTFE jacketed seal for the fluid side, conductive metal spring for the electrical side, both sharing one supplier's QC chain.
Comparison: PTFE material options against defense decision criteria
The four decision criteria that matter in defense are continuous temperature window, chemical compatibility, wear/creep under load, and SWaP penalty. Virgin PTFE wins on temperature (-200 to +260 °C) and chemical inertness, but loses on wear and creep [S1]. Filled PTFE (glass, carbon, bronze) wins on wear and creep but narrows the chemical envelope and pulls density upward from the 2.1-2.2 g/cm³ virgin baseline [S1]. Spring-energized PTFE jacketing wins on seal life because the spring keeps load on the lip even as the polymer wears, and the energizer geometry is what makes the seal "wear-regulating" rather than wear-limited [S2]. Canted-coil contacts win on SWaP because one spring replaces a fastener plus a separate conductor plus a separate EMI shield, three discrete parts collapsed into a single component [S2].
For platform architects, the rule of thumb is: specify virgin or near-virgin PTFE only where media is the binding constraint; specify filled PTFE only where pressure times velocity is the binding constraint; specify spring-energized PTFE whenever the duty cycle exceeds the polymer's standalone wear life; and specify canted-coil springs whenever the electrical/EMI interface sits next to the mechanical interface, as it does on most modern defense electronics boxes [S2]. For broader PTFE grade selection across non-defense industries, see PTFE selection for construction: grade, thickness, and spec gates and the upstream comparison PTFE Selection for Oil and Gas: Spec Gates, Grades, and Failure Modes, both of which apply the same density and shrinkage gating logic to civil projects.
Procurement data: density, shrinkage, moulding window, and what to put on the drawing
Three lines should appear on every PTFE defense part drawing: specific gravity 2.1-2.2 g/cm³ for virgin stock (move up to 2.3-3.0 g/cm³ bands for filled compounds, depending on filler), mould shrinkage 3.1-7.7% to drive the tool补偿 factor, and moulding temperature 330-380 °C to set the process window the molder must hit [S1].
Acme Plastics, which stocks high-performance engineering plastics for military and defense manufacturing, lists PTFE alongside polycarbonate, PEEK, and acetal in its defense material catalog, confirming that the same density-shrinkage gating logic applies across machined stock, sheet, and rod forms [S3]. The practical effect: a buyer who locks density and shrinkage first, then chooses filler family, can usually eliminate two of three vendors before any qualification testing starts.
Where PTFE is the wrong call in defense hardware
Virgin PTFE is the wrong material where the duty cycle is high-cycle dynamic sealing above ~1-2 m/s, where the system pressure drives lip extrusion, or where the part must hold a tight diametral tolerance without secondary machining; the 3.1-7.7% shrinkage band makes that combination unworkable [S1]. Filled PTFE is the wrong call where the media is a strong oxidizer that attacks the filler, where electrical insulation is required (most fillers raise conductivity), or where the lowest possible coefficient of friction is the binding requirement [S1].
Spring-energized PTFE jacketing is the wrong call in a static face seal where a simple O-ring or a metallic gasket can do the job at lower cost, and on any interface where the spring energizer cannot be assembled without dismounting the hardware, because the energizer geometry is the whole point of the design [S2]. Canted-coil contacts are the wrong call where the current per coil exceeds the spring's published ampacity, where the mating surface is too soft to take the spring's indentation, or where the EMI threat is so severe that a continuous metal gasket, not a point-contact spring, is required [S2]. These four negative gates are usually the fastest way to disqualify a candidate material before any environmental qualification testing is scheduled.
Sourcing and standards anchor points
Defense PTFE procurement maps to the same three reference anchors a buyer would use for any high-performance polymer: the polymer datasheet (density 2.1-2.2 g/cm³, shrinkage 3.1-7.7%, moulding 330-380 °C) [S1], the seal supplier's published functional spec covering friction control, media/temperature resistance, and wear-regulating spring behaviour [S2], and the defense plastics distributor's catalog confirming that PTFE is stocked alongside PEEK, polycarbonate, and acetal for military manufacturing [S3].
For adjacent platforms where the same gating logic applies, the medical-side PTFE Selection for Medical Devices: 2026 Spec Gates and oil-and-gas-side PTFE Selection for Oil and Gas: Spec Gates, Grades, and Failure Modes references carry comparable grade and failure-mode coverage. A general-purpose background page on the polymer itself is at PTFE.
Two trackable signals to watch: any published revision to a defense-qualified PTFE compound list from a major prime contractor (the effective change is usually a filler swap, not a polymer swap), and any new platform datasheet that pairs a PTFE seal with a canted-coil contact on the same interface, because that pairing is the current SWaP-driven design pattern in military avionics [S2].
Spec-level background on the components involved: pressure transmitter, and flow meter.