While today’s popular non-stick bakeware products manufactured out of Liquid Silicone Rubber (LSR) are flexible to the touch, they maintain a certain degree of resistance to deformation. While ear buds or in-ear headphones, on the other hand, require a close and comfortable fit with a flexibility that enables it to match the shape of the inner ear for a more natural feel.
Depending on the desired application of LSR, the hardness can be varied between 5-90 (Hardness, Shore A) by changing the cross-linker ratio. The hardness is measured as a function of penetration depth of an indenter. The indentation hardness is inversely related to the penetration (the higher the value, the softer the material) and therefore dependent on the elastic modulus and the viscoelastic behavior of the material.
There are twelve different types of hardness measurement devices (durometers) specified in ASTM D2240 or DIN 53 505: Types A, B, C, D, DO, E, M, O, OO, OOO, OOO-S and R. The letter implies a specific indenter geometry and applied force which has to be selected according to the maximum allowed penetration depth. For LSR, a Type A durometer is recommended in which the indenter should be loaded with a 1 kg weight. The hardness needs to be read within 1 second after the maximum indentation depth is reached.
 ASTM D 2240: Standard Test Methods for Rubber Property – Durometer Hardness; ASTM International, 2010
 Campo, E.A.: Industrial Polymers; Hanser Gardner Publications, Cincinnati, 2007
At SIMTEC Silicone Parts, a leading company in manufacturing high precision parts and components, we are exclusively focused and specialized in the production of LSR and LSR/Thermoplastic (Two-Shot) components.
Â© SIMTEC Silicone Parts, LLC
The information provided herein is to the best of our knowledge and it is believed accurate and reliable as of the date compiled. No representation, warranty or guarantee expressed or implied, is made as to the accuracy, reliability or completeness of the information provided herein. It is the user’s responsibility to determine the suitability and completeness of such information for the intended use. We do not accept liability for any loss or damage that may occur from the use of this information. Nothing herein shall be construed as a recommendation for uses which infringe valid patents or as extending a license under valid patents.