The Shore hardness of liquid silicone rubber (LSR) is a core indicator for measuring the material's resistance to indentation, usually measured using an A-type hardness tester, with a numerical range generally covering 0 to 90 degrees. In the development and selection process of LSR products, hardness is not an isolated physical parameter, it is directly related to the material's elastic modulus, tensile strength, and the final product's tactile feel. Choosing the appropriate Shore hardness for LSR is essentially about finding the best balance between mechanical properties, molding processes, and end use experience. For LSR materials in the low hardness range, i.e. below 10 degrees Shore A, their physical properties exhibit excellent softness and elongation.

This kind of material is close to human skin or gel in touch and has excellent deformation recovery ability. In terms of application selection, they are mainly used to manufacture products that require high adhesion and comfort, such as biomimetic prostheses in the medical field, pressure ulcer pads, and dust-proof and waterproof seals in high-end consumer electronics. Due to the low modulus of low hardness materials, they can undergo significant deformation without breaking when subjected to external compression, making them highly suitable for applications that require absorption of vibrations or filling of irregular gaps. The moderate hardness range, namely Shore A 10 degrees to 50 degrees, is currently the most widely used range for LSR applications. The material in this hardness range combines good flexibility with a certain degree of support, neither too soft to cause difficulty in demolding, nor too hard to lose elasticity. It is an ideal choice for manufacturing baby pacifiers, kitchen baking molds, wearable device straps, and conventional sealing rings.

When selecting hardness within this range, designers need to focus on the wall thickness and demolding slope of the product. Thinner wall thickness usually requires slightly higher hardness to ensure integrity during ejection, while complex inverted structures are suitable for selecting lower hardness to utilize the elastic deformation of the material for smooth demolding. When the Shore hardness exceeds 50 degrees or even reaches 70 degrees, LSR materials exhibit rigidity characteristics similar to thermoplastic materials. High hardness LSR has higher tear resistance and wear resistance, but significantly reduces elongation. This type of material is mainly used for components that require extremely high dimensional stability or need to withstand large mechanical loads, such as car ignition coils, high-voltage insulators, keyboard keys, and sealing rings for connectors.

When choosing high hardness LSR, it is important to note that its flowability is usually poor compared to materials with lower hardness, and higher injection pressure may be required to fill the mold cavity. In addition, the performance of high hardness materials in compression permanent deformation testing also needs to be evaluated in conjunction with specific formulations to ensure effective sealing rebound force can be maintained under long-term compression.

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