DuPont Kapton MT: Thermally Conductive Polyimide Film for Heat Management PCBs

The standard Kapton HN film that runs through most flex circuit and electronics insulation designs has a thermal conductivity of about 0.12 W/m·K. That’s adequate for electrical insulation, but when you’re designing a power electronics assembly, a motor slot insulation system, or a heat-sink pad for a dense PCB, 0.12 W/m·K is the thermal bottleneck that limits how much heat you can move through the dielectric layer. DuPont Kapton MT was developed specifically to break through that ceiling — delivering 0.46 W/m·K thermal conductivity, nearly 4× the standard Kapton HN, while preserving the electrical isolation, mechanical toughness, and temperature range that make polyimide the go-to dielectric in demanding electronics.

If you’re specifying an insulating dielectric for a thermal management application and you haven’t evaluated Kapton MT, this guide will give you the complete picture: specifications, available thicknesses, the MT vs. MT+ distinction, and where this film fits versus other thermal management options.

What Is DuPont Kapton MT?

DuPont Kapton MT is a thermally conductive polyimide film that is a homogeneous film possessing 3× the thermal conductivity and cut-through strength of standard Kapton HN. Its thermal conductivity properties make it ideal for use in controlling and managing heat in electronic assemblies such as printed circuit boards. Kapton MT offers an excellent combination of electrical properties, thermal conductivity, and mechanical toughness for its use in electronic and automotive applications.

Unlike Kapton HN, which uses a pure aromatic polyimide chemistry, Kapton MT incorporates thermally conductive filler material within the polyimide matrix. The result is a homogeneous film — not a laminate or coated construction — meaning the thermal conductivity is uniform through the thickness of the film rather than being a surface property. This homogeneous construction is important in practice because it means the film won’t delaminate under thermal cycling and the thermal performance doesn’t depend on interface quality between layers.

The Kapton MT family is also available as Kapton FMT, which combines the thermally conductive MT film with FEP fluoropolymer coating on both sides for heat sealability and improved chemical resistance — the same concept as the Kapton FN family but starting from the MT thermally conductive base.

For context on how Kapton MT fits within DuPont’s broader electronics materials lineup including laminates and specialty films, DuPont PCB covers the full portfolio.

The Kapton MT Family: MT, MT+, and FMT

DuPont has developed the Kapton MT into a three-member family, each addressing progressively more demanding thermal requirements:

Film	Thermal Conductivity	vs. Kapton HN	Primary Differentiator
Kapton HN	0.12 W/m·K	Baseline	Standard general-purpose polyimide
Kapton MT	0.46 W/m·K	~4×	Thermally conductive, high cut-through strength
Kapton MT+	0.75–0.80 W/m·K	~6–7×	Highest thermal conductivity polyimide film
Kapton FMT	~0.46 W/m·K	~4×	MT base + FEP fluoropolymer coating both sides

Kapton MT+ is the next-generation formulation possessing nearly 2× the thermal conductivity of Kapton MT and 4× (or higher) of Kapton HN while retaining superior electrical properties. The MT+ article positions it as the highest thermal conductivity film on the market for a polyimide construction. The FMT variant adds FEP coating to the MT base, enabling heat sealing capability for motor slot liner and sealed heater circuit applications.

Full Technical Specifications: Kapton MT

The following properties are from the official DuPont Kapton MT Technical Data Sheet (H-38497-3):

Mechanical Properties by Thickness

Property	100MT (1 mil / 25 µm)	150MT (1.5 mil / 38 µm)	200MT (2 mil / 50 µm)	300MT (3 mil / 76 µm)	Test Method
Tensile Strength, kpsi (MPa)	20 (138)	21 (145)	22 (152)	23 (159)	ASTM D882
Modulus, kpsi (GPa)	440 (3.0)	450 (3.1)	475 (3.3)	490 (3.4)	ASTM D882
Elongation (%)	80	85	87	100	ASTM D882
Tear Strength, initial (Graves), lbf	1.7	—	—	—	ASTM D1004
Cut-Through Strength, lb	40	—	—	—	DuPont Method

The higher modulus compared to Kapton HN (440–490 kpsi for MT vs. 370 kpsi for HN) is a direct result of the thermally conductive filler loading. This higher stiffness means Kapton MT offers improved strength to the final product — a practical benefit in slot liner and insulation pad applications where the film must maintain its shape under winding pressure and thermal cycling.

The cut-through strength specification (40 lb) is critical for motor slot insulation: slot liners must resist sharp edges on copper conductor wires that can pierce thin insulation under winding pressure. Kapton MT’s 3× higher cut-through strength versus HN directly translates to longer motor insulation life in high-current applications.

Electrical Properties

Property	Value	Thickness Note	Test Method
Dielectric Strength	5,500 V/mil (100MT)	Decreases with thickness	ASTM D149
Dielectric Strength	5,100 V/mil (150MT)	—	ASTM D149
Dielectric Strength	4,600 V/mil (200MT)	—	ASTM D149
Dielectric Strength	4,100 V/mil (300MT)	—	ASTM D149
Dielectric Constant (Dk) at 25°C	4.2	All thicknesses	ASTM D150
Surface Resistivity	> 10¹⁵ Ω/sq	All thicknesses	ASTM D257
Volume Resistivity	> 10¹⁶ Ω·cm	All thicknesses	ASTM D257

The dielectric constant of 4.2 is slightly higher than standard Kapton HN (3.4) because the thermally conductive filler material has a higher permittivity than the polyimide matrix. This is the expected trade-off with thermal filler loading and is well within the range acceptable for most power electronics insulation applications. For signal integrity on high-speed digital layers, the standard Kapton HN (Dk 3.4) is preferable; for power planes and thermal insulation pads, Dk 4.2 is not a concern.

The dielectric strength values (4,100–5,500 V/mil depending on thickness) remain strong — comparable to Kapton HN in the same thickness range — confirming that the thermal filler loading does not meaningfully compromise electrical isolation capability.

Thermal Properties

Property	Value	Test Method
Thermal Conductivity	0.46 W/m·K	ASTM D5470
Flammability	V-0	UL-94
Temperature Range	-269°C to 400°C	—
Storage Temperature	4–29°C (40–85°F)	Original packaging

The measured thermal conductivity of Kapton MT (0.46 W/m·K by ASTM D5470) has been independently validated at approximately 0.517 W/m·K using transient plane source (TPS) methods — within 5.6% of the supplier specification, confirming the datasheet value is conservative rather than inflated.

Kapton MT+ Specifications for Reference

When Kapton MT’s 0.46 W/m·K isn’t sufficient, Kapton MT+ pushes to 0.75–0.80 W/m·K:

Property	150MT+ (1.5 mil)	200MT+ (2 mil)	300MT+ (3 mil)	Test Method
Thickness, mils (mm)	1.5 (0.038)	2.0 (0.050)	3.0 (0.076)	ASTM D374
Tensile Strength, kpsi (MPa)	12 (83)	12 (83)	12 (83)	ASTM D882
Modulus, kpsi (GPa)	625 (4.3)	625 (4.3)	625 (4.3)	ASTM D882
Elongation (%)	44	44	35	ASTM D882
Dielectric Strength, kVAC/mil	5.3	5.0	3.9	ASTM D1491
Surface Resistivity (Ω/sq)	> 10¹⁵	> 10¹⁵	> 10¹⁵	ASTM D257
Volume Resistivity (Ω·cm)	> 10¹⁵	> 10¹⁵	> 10¹⁵	ASTM D257
Thermal Conductivity (W/m·K)	0.75	0.75	0.75	ASTM D5470
Flammability	V-0	V-0	V-0	UL-94

Note the higher modulus of MT+ (625 kpsi / 4.3 GPa) compared to MT (440–490 kpsi / 3.0–3.4 GPa) — a higher filler loading achieves higher thermal conductivity but also increases stiffness and reduces elongation (44% for MT+ 150MT+ vs. 85% for 150MT). This reduced elongation means Kapton MT+ is less suitable for tight-radius bending or dynamic flex applications but excellent for flat slot liner and pad applications.

Kapton MT vs. Kapton HN: The Thermal Engineering Case

Every power electronics engineer understands thermal resistance as R_th = thickness / (thermal conductivity × area). Swapping Kapton HN for Kapton MT at the same dielectric thickness (say, 1 mil / 25 µm) reduces the thermal resistance of the insulation layer by approximately 4×:

Parameter	Kapton HN (1 mil)	Kapton MT (1 mil)	Improvement
Thickness	25 µm	25 µm	Same
Thermal Conductivity	0.12 W/m·K	0.46 W/m·K	3.8×
Thermal Resistance (1 cm²)	2.08 K·cm²/W	0.54 K·cm²/W	3.8× lower
Dielectric Constant	3.4	4.2	Slightly higher
Cut-through Strength	Standard	3× higher	MT advantage

In a heat sink pad application where the PCB surface temperature is 80°C, a heat source dissipating 5W through a 1 cm² Kapton insulation pad would produce:

• With HN (0.12 W/m·K): ΔT across dielectric = 5W × 2.08 K·cm²/W / 1 cm² = 10.4°C temperature drop
• With MT (0.46 W/m·K): ΔT across dielectric = 5W × 0.54 K·cm²/W / 1 cm² = 2.7°C temperature drop

That 7.7°C difference at the dielectric layer is significant in power electronics where junction temperatures are critical. For a power module running close to its maximum junction temperature, recovering 7–10°C through a better insulation material can mean the difference between reliable operation and thermal failure.

Applications Where Kapton MT Delivers Real Performance

Insulation Pads for Heat Sinks

In power electronics assemblies where a semiconductor device mounts to a heat sink and needs electrical isolation, the dielectric pad between the device flange and the heat sink is the thermal bottleneck. Traditional solutions use ceramic-filled epoxy pads or mica sheets — both effective but bulky and fragile. Kapton MT at 1–2 mil provides a thin, flexible, tough alternative with 0.46 W/m·K thermal conductivity and high dielectric strength (4,600–5,500 V/mil).

Electric Motor Slot Insulation

This is where Kapton MT’s combination of thermal conductivity and cut-through strength is most compelling. In electric motors — especially the high-power density motors used in EVs and industrial drives — the copper windings generate significant heat that must conduct through the slot insulation to the stator lamination and cooling system. Kapton MT+ used as slot liner insulation can reduce operating temperature by 20–45°C in e-motors compared to standard slot liner materials. This temperature reduction directly enables either higher power density from the same motor or improved lifetime reliability at the same power level.

The Fraunhofer IFAM test program (reports A217279 and A218102) validated this improvement in real motor hardware, comparing standard slot insulation systems against Kapton MT+ laminates under controlled thermal and electrical stress conditions. This independent testing confirmation is important when specifying a material change for production motor programs.

Ceramic Board Replacement

In power electronics modules traditionally using ceramic substrates (alumina or AlN) for thermal management, Kapton MT provides a lightweight, flexible, cut-to-shape alternative. Where ceramic boards are brittle, thick, and require specialized drilling/machining, Kapton MT can be die-cut, laser-cut, or punched to shape on standard film processing equipment. The trade-off is lower thermal conductivity than ceramics (AlN at 170–200 W/m·K is far superior thermally), but for applications where the dielectric thickness can be reduced below the ceramic board and where the flexibility of polyimide enables simpler assembly, Kapton MT is a cost-effective alternative.

Heater Circuits and Power Supply Insulation

In flexible heater circuits where the resistive element is laminated between two dielectric sheets, Kapton MT improves the thermal uniformity and temperature uniformity of the heater by conducting heat laterally within the film plane as well as through-thickness. Power supply insulation at transformer and capacitor windings benefits from the same 4× thermal conductivity improvement.

Comparing Kapton MT to Competing Thermal Interface Materials

Material	Thermal Conductivity (W/m·K)	Dielectric Strength	Flexibility	Cut-Through Resistance
Kapton HN	0.12	303 kV/mm (1 mil)	Excellent	Standard
Kapton MT	0.46	216 kV/mm (1 mil)	Good	3× HN
Kapton MT+	0.75–0.80	209 kV/mm (1.5 mil)	Moderate	High
Alumina (Al₂O₃) ceramic	20–30	High	None — rigid	Brittle
AlN ceramic	170–200	High	None — rigid	Brittle
Ceramic-filled silicone pad	2–10	Moderate	Soft/compliant	Low
BN-filled epoxy laminate	1–5	Moderate–high	Rigid	Moderate

Kapton MT isn’t trying to compete with ceramics on thermal conductivity — it’s competing on the combination of thermal performance, electrical isolation, mechanical durability, flexibility, and processability. A 0.46 W/m·K insulator that you can die-cut, handle, and laminate like a standard polyimide film has fundamentally different manufacturing economics than a ceramic tile.

Useful Resources for PCB Engineers

Resource	Link
Kapton MT Technical Data Sheet (H-38497-3)	Materials Direct PDF
Kapton MT+ Data Sheet (EI-10218)	DuPont PDF (via dupont.com)
Kapton MT and MT+ Product Pages (Qnity/DuPont)	qnityelectronics.com — Kapton MT+
Fraunhofer IFAM Test Report A218102 (EV Motor Validation)	Available via DuPont/Qnity technical support
Fralock — Kapton Film Reference and Products	fralock.com
Thermtest — Kapton MT Thermal Conductivity Measurement	thermtest.com
DuPont PCB Materials Overview	pcbsync.com/Dupont-pcb
IPC-4202 — Flexible Base Dielectrics for Flex PCBs	ipc.org
ADDEV Materials — Kapton Film Ranges Overview	addevmaterials.us

5 FAQs About DuPont Kapton MT

Q1: What is the difference between Kapton MT and Kapton MT+? Kapton MT has a thermal conductivity of 0.46 W/m·K — approximately 4× standard Kapton HN. Kapton MT+ is the next-generation formulation with a thermal conductivity of 0.75–0.80 W/m·K, which is nearly 2× the MT and over 6× the baseline HN. The MT+ achieves higher conductivity through a higher filler loading, which also results in a higher modulus (625 kpsi for MT+ vs. 440–490 kpsi for MT) and lower elongation (35–44% for MT+ vs. 80–100% for MT). The practical consequence is that MT+ is stiffer and less flexible than MT — appropriate for flat pad and slot liner applications, but less suitable for tight-radius bending.

Q2: Can Kapton MT be used as a flex circuit base substrate? Kapton MT can be processed in flex circuit manufacturing lines — it can be metallized, etched, and laminated — but it is not the standard specification for typical flex PCB substrates. Its higher dielectric constant (4.2 vs. 3.4 for HN) introduces slightly higher capacitance coupling between conductors, and its reduced flexibility compared to HN means it’s better suited for applications with gentle bends rather than dynamic flex. For signal-carrying flex circuits, specify Kapton HN or Kapton FPC. For power-carrying flex circuits where thermal management is the primary concern, Kapton MT may be the right choice — evaluate both thermal and signal integrity requirements together.

Q3: How do I calculate the thermal improvement from switching from Kapton HN to Kapton MT? Use the thermal resistance formula: R_th = t / (k × A), where t is dielectric thickness, k is thermal conductivity, and A is the area. For a 1 mil (25 µm) pad at 1 cm² area: R_th for HN = 0.025 mm / (0.12 W/m·K × 0.0001 m²) = 2.08 K/W. For MT at the same thickness: R_th = 0.025 mm / (0.46 W/m·K × 0.0001 m²) = 0.54 K/W. The temperature drop across the dielectric is ΔT = P × R_th. At 5W dissipation, the HN creates a 10.4°C drop vs. 2.7°C for MT — a 7.7°C improvement from the dielectric alone. For higher power densities or larger thermal budgets, this difference compounds significantly.

Q4: Is Kapton MT suitable for EV motor slot insulation? Yes — and this is one of the most important emerging applications for Kapton MT and MT+. Fraunhofer IFAM validated in independent testing that Kapton MT+ slot liner systems reduce winding operating temperatures by 20–45°C compared to conventional slot insulation materials. This temperature reduction is significant because every 10°C reduction in insulation temperature roughly doubles the insulation lifetime (per Arrhenius degradation models). For EV motor programs targeting high power density and long service life, Kapton MT+ slot liners offer both performance and durability benefits over traditional Nomex/polyester slot liner systems.

Q5: Does Kapton MT meet the same military and IPC specifications as Kapton HN? Kapton HN is qualified to ASTM D-5213 (type 1, item A), Mil-P-46112, and IPC-4202/1. Kapton MT, as a thermally filled variant, meets IPC-4202 as a flexible dielectric base material but carries its own product specifications (H-38497-3) rather than the HN general specifications. For military procurement requiring Mil-P-46112 qualification specifically, verify with DuPont/Qnity whether the current Kapton MT specification is covered under that military spec or requires a separate qualification. For commercial electronics and automotive applications, the DuPont technical datasheet (H-38497-3) and IPC-4202 coverage are typically sufficient.

Engineering Perspective

DuPont Kapton MT occupies a specific and valuable position in thermal management material selection: it’s the polyimide insulation film you reach for when standard Kapton HN creates a thermal bottleneck that 0.12 W/m·K can’t solve, and when the application doesn’t have the form factor or budget for ceramic substrates. The 4× improvement in thermal conductivity at the same dielectric thickness, combined with 3× cut-through strength and retained electrical isolation, makes it particularly well-suited for power electronics insulation pads, motor slot liners, and any assembly where the dielectric layer carries both electrical isolation and heat transport duties simultaneously. For the most demanding thermal applications — high-power-density EV motor windings, compact power modules — Kapton MT+ pushes to 0.75–0.80 W/m·K and adds the Fraunhofer-validated 20–45°C temperature reduction in real motor hardware that no spec sheet alone can claim.