eVTOL & Advanced Air Mobility: Battery Thermal, Fire-Barrier, EMI & Sealing Materials

Three converted graphite layers do most of the work. SpreaderShield flexible graphite fins sit between cells, spreading heat laterally and acting as propagation barriers; eGRAF HiTherm graphite TIM couples the cell stack to the liquid cold plate, with a listed service range of −40 to +400 °C on the pure-graphite HT-12xx grades (−25 to +125 °C on the polymer-enhanced HT-25xx grades) per the maker’s TDS; and a pure-graphite gasket seals the module perimeter. Dielectric TIM pads carry the inverter and BMS interfaces that must electrically isolate. [12]

Flexible graphite is direction-engineered: in-plane thermal conductivity is far higher than through-plane. A fin between two cells therefore moves heat away laterally, toward the cold plate and module walls, faster than it lets heat cross to the neighboring cell. In normal flight that kills hot spots; in a thermal event the same inorganic ply, which has no organic binder to burn away, buys time for the barrier stack around it. Per-grade values are on the NeoGraf TDS. [12]

Because of what a flight profile does to a joint. Greases rely on a liquid phase: joints that breathe with vibration and thermal cycling pump the grease out, and long service dries it. A graphite TIM sheet has no liquid phase, so the interface it makes on day one is the interface it keeps, with thermal impedance framed per ASTM D5470 at stated clamp pressure on the TDS. It is also to the exact stack footprint, which keeps assembly repeatable. [7]

A pure-graphite perimeter gasket. Elastomer seals char and lose their body in a thermal event; flexible graphite is inorganic, carries no binder to burn away, and does not melt in service terms, so the seal that kept water out on Tuesday is still holding hot gas back during the event. Where the same joint needs electrical isolation, the graphite ring pairs with a mica or ManniGlas backing ply. Per-grade limits are on the maker’s TDS. [12]

In layer order: graphite fins at the cell wall; ManniGlas glass-fiber paper (UL 94 V-0 listings per TDS) at module walls and lids; mica sheet where the barrier must also be a dielectric; ArmaGel HT aerogel, in the low-0.02 W/m·K class per ASTM C177 on its TDS, where the envelope is tightest; and purpose-built EV firewall laminates such as ProCell constructions between modules and at the pack boundary. The ordered set, not any single layer, is the mitigation. [10] [5]

Only with a designed dielectric boundary. Graphite conducts electricity, so every fin, TIM, and gasket near terminals or busbars gets a Kapton or Apical film ply, or a dielectric-coated graphite construction, engineered into the part, ideally laminated so the boundary cannot be omitted at assembly. Breakdown data for the films is per ASTM D149 on the TDS. Where the isolation scheme cannot be confirmed, the interface moves to a dielectric TIM pad instead. [9]

Conductive silicone elastomers framed by MIL-DTL-83528 per the maker’s documentation: the SSP502 family, with a fluorosilicone base for fluid-exposed joints, a flame-retardant V-0 variant, and a corrosion-resistant filler for bare aluminum flanges, where galvanic compatibility decides service life. Conductive foil tapes bond seams, and EC-2130 conductive sponge covers low-closure-force doors. Shielding values are per the material TDS; the installed attenuation belongs to the tested enclosure. [6]

Every climb and descent cycles the pressure differential across a sealed enclosure, so the gasket is asked to breathe thousands of times, not to squeeze once. That promotes compression-set resistance, framed by ASTM D1056 data on the TDS, above initial firmness, and it often adds an ePTFE vent membrane that equalizes pressure across the wall so the gasket stops being the breathing path. Ingress ratings are earned by the tested enclosure, not claimed by a material. [11]

Nomex aramid paper for slot liners and phase barriers, used in insulation systems up to Class R (220 °C) practice per the maker’s documentation; Kapton polyimide film for the thin, high-breakdown-strength plies and busbar wrap; and Nomex-Kapton laminates where a slot needs mechanical body and film strength in one part. High-frequency PWM drive adds repetitive voltage stress, so the film’s per-grade breakdown data per ASTM D149 matters as much as the thermal class. [13]

H-O converts materials whose makers publish FST test data referenced to those benchmarks, SOLIMIDE polyimide foam aerospace grades are the flagship, along with ManniGlas backing plies, kSil KSV001–KSV006 silicone sponge (FAR 25 Appendix F, ABD0031, smoke and toxicity data per TDS) and flame-rated BISCO silicone foams, and ships them with per-grade TDS documentation and lot traceability. The compliance finding itself always belongs to the aircraft-level test and the certification applicant; H-O supplies the converted part and the maker’s data behind it, and makes no airworthiness claims. [3] [4]

Same physics, harder consequences and a harder weight budget. A road vehicle in a thermal event can stop; an eVTOL must contain and manage the event through a landing, which pushes barrier stacks to more layers and inorganic chemistry. Every gram of material repeats across cells, modules, and rotors, so gauges are engineered rather than defaulted. And qualification runs through aviation framings, DO-160 environments and the consolidating SC-VTOL / powered-lift criteria, instead of automotive test plans. [2] [1]

The part outline and gauge with tolerances; the job direction (spreader vs. TIM vs. barrier); the barrier layer order if the part sits in the stack; the electrical isolation requirement and any bounded-construction call-out; clamp pressure or fastener pattern and torque for TIM joints; the temperature window and fluid exposure; the flammability or FST benchmark by designation; adhesive and liner requirements; and prototype plus annual volumes. That set lets material review verify the working point against each TDS in one pass.

Samples typically ship in 3–5 business days for common configurations in materials we commonly convert, and typical prototypes run 5–10 business days after drawing review. Standard production runs ship about 2 weeks after drawing approval, including kiss-cut-on-liner and laminated barrier stacks. Everything is made-to-order and MOQ varies by material and part, so unusual constructions are quoted with their own timeline up front.

H-O Products is an ISO 9001:2015 certified organization; the certification covers the quality management system, not any product. H-O does not claim aerospace-specific quality registrations. Parts ship with material traceability and lot-code TDS records, and material certifications and per-grade test data come from the source manufacturers’ documentation. Airworthiness and system qualification remain with the aircraft OEM and integrator, which is the honest division of labor a certification audit expects to see.