Dk 3.38 in a filled PTFE laminate: how a moderate dielectric constant buys narrower lines, and where RT/duroid 4003C beats its lower-Dk sibling.
Rogers RT/duroid 4003C is a filled PTFE laminate for RF and microwave designs, and its distinguishing feature is a dielectric constant of about 3.38. That is higher than the 2.94 of its close relative, which changes the engineering story: for a given characteristic impedance the conductor can be narrower, so the layout is more compact. Around that number sit low dielectric loss, good thermal stability and mechanical toughness. Designs that lean on these properties appear across communications, radar and aerospace, and the family context is set out in our RT/duroid 3003 advantages article.
The two laminates come from the same family but serve different design intents. The table below sets the headline numbers side by side.
| Parameter | RT/duroid 3003 | RT/duroid 4003C |
|---|---|---|
| Dielectric constant (Dk) | approx. 2.94 | approx. 3.38 |
| Dielectric loss (Df) | below 0.003 | below 0.002 |
| Thermal weight loss temperature | approx. 300°C | approx. 300°C |
| Water absorption | Low | Low |
| Engineering implication | Widest lines for a given impedance; lowest loss | Narrower lines for a given impedance; denser layout |
Thermal weight loss temperature reaches about 300°C (572°F), so the laminate keeps its electrical performance under high-temperature processing and in service. Thermal conductivity is relatively high for a PTFE composite, which pulls heat away from components and lowers the risk of a hotspot turning into a field failure — the same mechanism that makes thermal design the deciding factor in communication equipment applications.
Chemical resistance covers the solvents, acids and alkalis met during fabrication and in the field. Low water absorption is the property that matters most for high-frequency work: it stops humidity from shifting the dielectric constant, so signal stability does not depend on the weather or the enclosure. That combination — stable Dk, low absorption, chemical resistance — is what makes 4003C usable in medical imaging and monitoring equipment, where performance has to be predictable rather than merely adequate.
Where the higher Dk is an advantage, 4003C tends to appear:
RT/duroid 4003C earns its place where a moderate dielectric constant, low loss and mechanical toughness have to coexist — particularly on boards that need to be compact as well as electrically clean. If the design prioritises minimum attenuation and can accept wider lines, RT/duroid 3003 is the closer fit. If the constraint is fabrication economics instead, the hydrocarbon laminates in the RO4000 series process more like FR-4 and are worth pricing before the stack-up is frozen.
Common questions about RT/duroid 4003C.
Approximately 3.38, with dielectric loss below 0.002. The moderate Dk reduces attenuation while allowing narrower conductors than a lower-Dk laminate would need for the same characteristic impedance.
The Dk is the headline difference: 3.38 against 2.94. 3003 gives the lowest attenuation with wider lines; 4003C allows a denser layout at a given impedance. Both hold a thermal weight loss temperature near 300°C with low water absorption.
Yes. The laminate is compatible with standard soldering processes including lead-free reflow, and it can be laser cut or etched where high-precision structural processing is required.
Moisture changes the dielectric constant, which shifts the impedance of every transmission line on the board. Low absorption keeps performance stable across humidity changes rather than only under laboratory conditions.
Communication equipment, radar, RFID, medical imaging and aerospace payloads — anywhere that needs stable high-frequency performance in a compact layout and can tolerate a higher Dk than the 3003 grade.
Send us the frequency plan, impedance targets and board outline. We will run the comparison across the 3003, 4003C and RO4000 options and quote the stack-up that fits your design intent.
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