橡楚编辑部 9/1/2026 45 min read
This article systematically sorts out the core characteristics of low-hardness silicone products, including high elasticity, skin-friendly touch, and excellent shock absorption performance. It also analyzes common process pain points in production such as mold sticking and dimensional control difficulties, shares corresponding solutions, and summarizes typical application scenarios in medical care, wearable devices, maternal and infant products, providing practical references for industry practitioners in material selection and production optimization.
Low-hardness silicone products, defined as liquid silicone rubber (LSR) or high-consistency rubber (HCR) formulations with a Shore A hardness of ≤30, or in many ultra-soft applications, Shore 00 scale ratings as low as 00-10, represent one of the fastest-growing segments of the silicone manufacturing industry. Unlike conventional silicone materials that typically range from Shore A 40 to 70, these low-hardness variants combine the inherent advantages of silicone—including biocompatibility, thermal stability, and chemical resistance—with exceptional elasticity, skin-like tactile properties, and minimal compression set. These unique characteristics have driven widespread adoption across medical devices, consumer wearables, automotive sealing systems, and industrial vibration damping components, where softness and long-term performance are non-negotiable requirements.
Recent market data from the Silicone Industry Association indicates that global demand for low-hardness silicone products is projected to grow at a 7.2% CAGR through 2030, outpacing the 4.8% growth rate of standard silicone goods. This surge is primarily fueled by the expansion of wearable medical monitors, premium consumer electronics, and electric vehicle (EV) noise, vibration, and harshness (NVH) systems. However, manufacturing low-hardness silicone products presents unique technical challenges, from formulation stability to demolding integrity, that distinguish it from standard silicone production. This analysis provides a comprehensive overview of low-hardness silicone material science, manufacturing optimization, key application performance requirements, and emerging innovation trends for industry stakeholders.
The unique properties of low-hardness silicone products originate from precise adjustments to the polymer backbone, crosslinking density, and additive systems of silicone raw materials. Unlike standard silicone formulations, where hardness is controlled by increasing filler content and crosslink density, low-hardness variants require a balanced approach to reduce hardness without compromising mechanical stability or long-term performance.
The foundation of low-hardness silicone is a high-molecular-weight polydimethylsiloxane (PDMS) polymer matrix with a linear chain structure and minimal branching. The molecular weight of the PDMS base directly impacts the final material’s softness and mechanical strength: formulations targeting Shore 00-10 to Shore A 10 typically use PDMS with a molecular weight of 600,000 to 800,000 g/mol, while Shore A 20 to 30 products use 400,000 to 600,000 g/mol PDMS to balance softness and tear resistance.
Crosslinking systems for low-hardness silicone are optimized to create a sparse, uniform network that allows maximum chain mobility while preventing permanent deformation. Most commercial low-hardness LSR formulations use platinum-catalyzed hydrosilylation curing, with a carefully controlled vinyl-to-hydride (Si-Vi/Si-H) molar ratio between 1:0.8 and 1:0.9, compared to a 1:1.1 ratio for standard hardness LSR. This reduced crosslinker content lowers crosslink density, increasing elasticity and reducing hardness. For ultra-soft formulations (≤Shore 00-20), manufacturers often incorporate long-chain difunctional crosslinkers with 20 to 50 dimethylsiloxane units between reactive ends, rather than the short 2 to 5 unit crosslinkers used in standard silicone, to further extend the distance between crosslink nodes.
Table 1: Core Formulation Parameters for Common Low-hardness Silicone Grades
Reinforcing fillers, typically fumed silica, are a critical component of silicone formulations, but high filler content increases hardness, requiring careful optimization for low-hardness grades. Standard silicone formulations use 25 to 35 wt% fumed silica, while low-hardness grades limit silica content to 3 to 18 wt%, depending on the target hardness. To compensate for the reduced mechanical strength from lower filler loading, manufacturers use surface-treated fumed silica with hexamethyldisilazane (HMDS) or polydimethylsiloxane coatings, which improve dispersion in the PDMS matrix and enhance filler-polymer bonding without increasing crosslink density.
Plasticizers are another key component of most low-hardness silicone formulations, used to reduce intermolecular friction between PDMS chains and increase softness. Non-reactive methyl phenyl silicone oil with a viscosity of 500 to 1000 cSt is the most common plasticizer, as it is highly compatible with PDMS and has minimal leaching potential. For medical-grade low-hardness silicone, reactive plasticizers with terminal vinyl groups are preferred, as they covalently bond to the crosslink network during curing, eliminating the risk of plasticizer migration into bodily fluids or food contact surfaces.
Additional additives include:
Low-hardness silicone products are evaluated against a distinct set of performance metrics compared to standard silicone, as their softness and elasticity are often critical to end-use functionality. The most important performance parameters include:
For example, low-hardness silicone used in cardiac pacemaker lead insulation must meet ISO 10993 biocompatibility requirements, maintain Shore A 25 hardness ±2 units after 10 years of implantation, and have a tear strength ≥15 kN/m to resist damage during surgical placement.
Manufacturing low-hardness silicone products presents unique challenges compared to standard silicone, as the soft, low-modulus material is prone to deformation during demolding, flash formation, and uneven curing. Process optimization is critical to achieve consistent dimensional accuracy, reduce scrap rates, and maintain material performance.
Injection molding is the most common manufacturing method for mass-produced low-hardness silicone products, including wearable wristbands, medical sealing gaskets, and automotive NVH components. The low viscosity of low-hardness LSR (typically 10,000 to 50,000 cP, compared to 100,000 to 500,000 cP for standard Shore A 50 LSR) requires precise control of injection parameters to prevent flash and short shots.
Key injection molding parameters optimized for low-hardness silicone include:
Mold design is equally critical for low-hardness silicone molding. Molds are typically fabricated from polished P20 or S136 steel with a surface roughness ≤Ra 0.2 μm to reduce adhesion between the soft silicone and mold surface. Draft angles are increased to 3° to 5° per side, compared to 1° to 2° for standard silicone, to facilitate demolding without part deformation. For parts with undercuts, collapsible core inserts are preferred over manual side actions, as the soft material can tear during manual demolding.
Even with optimized molding parameters, low-hardness silicone parts require specialized post-curing and demolding processes to maintain dimensional accuracy and performance. Demolding of ultra-soft parts (≤Shore 00-30) is typically performed using compressed air ejection at 2 to 3 bar pressure, rather than rigid ejector pins, which can puncture or deform the soft material. For complex geometries with small features, manufacturers may use water-soluble mold coatings that dissolve in deionized water after curing, eliminating the need for mechanical ejection entirely.
Post-curing is performed in a forced-air oven at 150°C to 180°C for 2 to 4 hours, depending on the part thickness, to complete crosslinking, remove residual volatile organic compounds (VOCs), and reduce compression set. For medical-grade parts, post-curing is performed under vacuum to minimize extractable content to meet USP Class VI requirements. After post-curing, parts are allowed to cool to room temperature in a controlled 23°C, 50% RH environment for 24 hours before dimensional inspection, as low-hardness silicone has a higher coefficient of thermal expansion (2.5×10⁻⁴ °C⁻¹) than standard silicone, and measurements taken immediately after post-curing will be inaccurate.
Flash removal is another key post-processing step for low-hardness silicone. The low viscosity of the material often leads to thin, soft flash along parting lines that is difficult to remove with standard tumbling or cryogenic deflashing. Most manufacturers use laser deflashing for precision low-hardness parts, with a 1064 nm fiber laser set to 20 to 30 W power, which vaporizes flash without damaging the part surface. For high-volume consumer products, water jet deflashing with 100 to 150 bar pressure and 100 μm abrasive media is used, reducing deflashing time by 70% compared to manual trimming.
Low-hardness silicone products are prone to three primary defects that are rare in standard silicone production, each requiring targeted mitigation strategies:
The unique combination of softness, biocompatibility, and long-term durability has led to the adoption of low-hardness silicone products across a diverse range of high-growth industries, each with distinct performance requirements tailored to their use case.
Low-hardness silicone is the material of choice for a wide range of medical devices, where softness reduces patient discomfort, biocompatibility enables long-term skin or tissue contact, and elasticity ensures a secure seal or fit. The most common medical applications include:
Table 2: Performance Requirements for Medical Grade Low-hardness Silicone
The global wearable device market, projected to reach $186 billion by 2027, is one of the largest drivers of low-hardness silicone demand, as manufacturers prioritize user comfort and tactile experience for devices worn 24 hours a day. Key applications include: