Thermoset Composites Are Not Dead: Their Enduring Value in Modern Engineering

Although it may appear a recent trend, the quiet competition between thermoset composites and thermoplastics has been unfolding since the late 1980s. Engineers weigh the advantages and disadvantages of each material as intensely as tech enthusiasts debate Microsoft versus Linux. The debate continues, with some proponents labeling composites as “dead” while others assert that both materials have distinct, valuable roles—and that thermoset composites are far from extinct.

Critics point to thermosets’ limited shelf life and poor recyclability after curing. Once a catalyst initiates cross‑linking, the molecular structure becomes permanent and irreversible. When exposed to heat, the material degrades rather than melts, because it breaks down below its melting temperature. Consequently, manufacturers must precisely control the polymerization process, as a cured thermoset cannot be remelted or reshaped.

Thermoplastics, in contrast, are praised for their ease of processing: they melt, pour, solidify, and remelt repeatedly. So why aren’t thermoplastics ubiquitous across the industry? Why do engineers still favor thermoset composites in certain applications?

1. Thermosets have a long, proven track record and are deeply entrenched in the market.
2. They offer lower raw‑material costs.
3. They enable simpler forming and processing techniques.
4. They provide superior thermal resistance, making them ideal for brake pistons, jet‑engine components, and high‑performance supercars.
5. Thermosets constitute about 95 % of aerospace prepreg supplies.

Thermoset composite parts are typically made from epoxy or polyester resins, most often reinforced with glass fibers. Depending on the application, polyester systems can be cured to produce either softer, more flexible or harder, more brittle composites. Polyester composites are found in a wide range of consumer and industrial products—from bathroom showers to automotive body panels to boat hulls. In the electrical sector, thermosets offer a dielectric advantage that benefits both arc and track‑resistance applications.

Epoxy resins are cured to achieve a hard, tough matrix with excellent resistance to solvents and alkalis, making them ideal for glass‑reinforced circuit boards.

While glass dominates as a reinforcing fiber, thermoset composites also incorporate carbon, graphite, boron, and aramid (Kevlar) fibers, selected based on the specific performance requirements.

Thermoplastics continue to evolve, mirroring the historical progression of thermosets. However, they are not displacing thermosets entirely. Thermosets remain trusted in aerospace and automotive sectors, while thermoplastics steadily expand into those markets.

Rather than positioning one technology against the other, the future will likely see each material applied where it excels, and replaced only when a superior competitor emerges—much like Microsoft’s dominance on the desktop and Linux’s strengths at the network edge.