Tubing Buying Tip #11: Hardness/Softness/Durometer
What’s the appropriate tubing softness or hardness for your application?
Tubing hardness is measured as its durometer. Different instruments and durometer scales, namely Shore A, Shore D, and Rockwell R are commonly used to measure the hardness of plastic (thermoplastic) and rubber (thermoset) materials. The lower the number on the scale, the softer and more flexible the material is.
For example, silicone tubing is a very soft and pliable product. A typical hardness rating for it is 50 Shore A (also stated as Shore A50). Our polyurethane tubing is not as soft as silicone and can measure 70-95 Shore A. Rigid and semi-rigid tubing materials like nylon and polyethylene are normally measured on the Shore D scale, but the same numbering pattern applies: the lower the durometer number, the softer the tubing. Actual ratings for this type of tubing vary widely due to different material formulations (i.e., high-density polyethylene and linear low-density polyethylene). Harder plastic materials, such as polypropylene, use the Rockwell R scale.
All three scales overlap at a point (the high end of Shore A, the low end of Shore D, and the extreme low end of Rockwell R). The determination regarding which scale is used depends on factors such as popularity in different locales and what is common in a specific industry or learning environment.
Flexibility and softness – or hardness – requirements differ from one application to the next, so the needs of your particular project must be carefully considered. In general, softer tubing materials are more flexible and may be less prone to kinking.
Harder tubing generally offers reduced friction and allows items to glide easily across the surface. This type of tubing is more appropriate than soft tubing for applications such as adhesive transfer. A rigid or semi-rigid tube can be useful when tubing needs to be stiff and supportive.
The types of fittings needed to make connections change depending on tubing hardness, as does the necessity for clamps. Soft tubing often uses barbed fittings with clamps, although heavy-duty softer tubing may call for cam-operated couplings secured with clamps. Semi-rigid and rigid tubing styles employ push-to-connect or compression fittings, and multi-layered reinforced hose can require fittings that are permanently crimped on with collars.
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