How is the "softness" (durometer) of medical grade silicone measured?
This is a question that comes up almost every day when discussing new project ideas with perspective clients. The softness or durometer of all polymers/elastomers/rubbers is measured essentially the same way and the term while commonly used to describe the material hardness, actually originated from the device used to take the measurement a duro-meter. There are lots of different designs for this device, click here to compare pricing and options and get a general feel for what they look like and how they work.
A material's softness is described by its resistance to deformation when exposed to a known, measurable force. When the needle of the durometer tester (as they are often referred to nowadays) is pushed into an elastomer (like medical grade silicone) the material pushes back with a certain amount of force that will read out on the dial in the form of a "durometer." A certain amount of skill and experience are required to receive accurate readings. You must also make sure to have a large enough sample of material to measure, otherwise you end up taking a durometer reading on the table underneath your silicone part.
Since there are such drastic differences from one material to the next in terms of hardness (compare a gel insole for a shoe to a hockey puck) there were different scales or "Shores" for the durometers to be measured in. While there are about a dozen different shores, the commonly used ones in our industry are Shore A, Shore D, and Shore OO. These Shore scales do overlap, and the image below does an excellent job of providing real world examples that people are exposed to throughout everyday life.
The reason these different scales are referred to as Shores is due to the scientist Albert F. Shore who is credited with the development of this measurement system. Click here for more information on durometer.
If you have further questions on durometer, we would love to help. Email Kevin Franzino at firstname.lastname@example.org.