HDT (Heat Deflection Temperature)

Heat Deflection Temperature (HDT) is a critical property of polymers, including those used in resin 3D printing and polymer additive manufacturing. It refers to a polymer’s ability to remain rigid or “stiff” under a constant load and elevated temperatures. It indicates at what temperature a polymer starts to “soften” under a fixed load.

HDT is crucial in determining a material’s maximum temperature for structural applications. It is a helpful gauge for determining the temperature at which a material cannot be used for structural applications. This value can be used to compare materials with one another. It also helps indicate how a plastic part will perform when placed under mechanical load and exposed to heat.

In the context of resin 3D printing, HDT can be a bit misleading. Many photopolymers have a high HDT on the spec sheet, but undergo chemical reactions when heated that compromise the material performance. In this case, the spec sheet HDT might look high, but it is not actually representative of the true working temperature of the material.

HDT is in some ways very arbitrary, it is reported at a specific load for a specific bar geometry. It is not a fundamental property of the material, but rather a useful metric for comparing materials.

Your choice of material depends on the specific application and operating conditions. For example, if a 3D-printed part will be used under a load in high-temperature environments, it must have a high HDT value to maintain its shape and properties.

In summary, the Heat Deflection Temperature is a key factor in the selection of materials for resin 3D printing and polymer additive manufacturing, influencing the performance, durability, and application of the final product.

• COR Alpha: HDT @ 0.455 MPa is 139 °C and @ 1.82 MPa is 132 °C (source)
• COR Black: HDT @ 0.455 MPa is 138 °C and @ 1.82 MPa is 129 °C (source)

Related: Glass Transition Temperature (Tg)