MATERIAL SCIENCE GUIDE

A Guide to Thermal Properties

How a material behaves with heat is critical for many applications. This guide explains the key thermal properties that govern performance in both hot and cold environments.

Key Thermal Properties Explained

Thermal Conductivity

This measures a material's ability to transfer heat. Materials with **high thermal conductivity** (like copper and aluminum) are excellent for pulling heat away from a source, making them ideal for heat sinks. Materials with **low thermal conductivity** (like most plastics) are thermal insulators, good for creating barriers to stop heat transfer.

Heat Resistance

This is a material's ability to maintain its strength and stiffness at elevated temperatures. It's often measured by the **Heat Deflection Temperature (HDT)** or the **Continuous Use Temperature**. High-performance materials like PEEK, Ultem™, and Inconel excel in this area.

Coefficient of Thermal Expansion (CTE)

This measures how much a material expands when heated and contracts when cooled. A low CTE means the material is dimensionally stable across a range of temperatures. This is critical for precision parts in assemblies with different materials, as a mismatch in CTE can cause stress and failure.

Materials for Thermal Management

Best Conductors (for Heat Sinks): Copper is the best thermal conductor among common metals, making it the top choice for high-performance heat sinks. Aluminum offers excellent conductivity for its weight and cost.
Best Insulators (for Thermal Barriers): Most plastics are thermal insulators. PEEK and Ultem™ are excellent choices as they combine low thermal conductivity with high heat resistance.
Best for Stability (Low CTE): Carbon fiber composites, ceramics, and metals like steel have very low CTE. For plastics, adding glass or carbon fibers significantly lowers the CTE and improves stability.

A CNC machined copper heatsink, an application where thermal conductivity is the key property

Thermal Properties FAQ

My part is warping when it gets hot. What is happening?

This is likely because the operating temperature is exceeding the material's Glass Transition Temperature (Tg) or Heat Deflection Temperature (HDT). The plastic is softening and deforming under load. You need to select a material with a higher heat resistance, such as moving from ABS to Polycarbonate, or from Polycarbonate to Ultem™.

What does "thermal runaway" mean for a CNC machine?

When machining a material with low thermal conductivity like Titanium, heat does not escape with the chip. It builds up in the tool, causing it to soften and get dull. A dull tool generates even more friction and heat, which makes the tool duller still. This feedback loop is called thermal runaway and can quickly destroy a cutting tool if not managed with proper speeds and high-pressure coolant.