What does ‘HDT’ mean and why is it important as it relates to Smooth-On rubber, plastic or expanding foam products?

HDT is an abbreviation for “Heat Distortion Temperature” or “Heat Deflection Temperature” as it relates to these types of materials.  It measures a material’s ability to resist a force (flexing or a weight pressing down) on a swatch of material when exposed to different temperatures. 

Diagram Description automatically generatedFor example, the HDT of a 40A durometer urethane rubber is below 32°F / 0°C, as a swatch of the rubber that measures 6” x 1”  0.25” (15.24cm x 2.54cm x .64 cm) will have some flexibility. A general purpose liquid plastic with the same dimensions that has a durometer of 85D (such as Smooth-Cast™ 385) will be rigid and unbendable at 32°F / 0°C.

Know that different materials have different HDT’s and that choosing a material that has an insufficient HDT for your specific application can result in material failure  Recommended; if the cured material you will be using for your application will be exposed to elevated temperatures, either direct or indirect, know the HDT of the material you are considering before you purchase.

This FAQ article is offered as a guideline and offers possible solutions to problems encountered during mold making and casting. No warranty is implied and it is up to the end user to determine suitability for any specific application. Always refer to the provided Technical Bulletins (TB) & Safety Data Sheets (SDS) before using any material. A small scale test is suggested to determine suitability of any recommendation before trying on a larger scale for any application.