Silicone Rubber Grade Selection Guide

Silicone Rubber Grade Selection Guide

Selecting the correct silicone rubber grade is a structured decision process that starts with application requirements and ends with a specific compound designation from a qualified supplier. This guide walks through the decision tree from application type to final grade specification.

Step 1: Select the Correct Silicone Form

The first decision is which form of silicone rubber the application requires:

HTV (solid compound) → Extrusion, compression molding, calendering LSR (liquid, two-part) → Injection molding, complex geometries, high volume RTV-1 (one-part) → On-site sealing, repair, construction RTV-2 (two-part liquid) → Mold making, potting, casting

If the application involves a continuously produced extruded profile or cable, HTV is the only option. If the application requires injection molding into complex shapes at volumes above 50,000/year, LSR should be evaluated.

Step 2: Determine Shore Hardness

Match the hardness to the application's functional requirements:

If in doubt, start with Shore 50A for general sealing applications and adjust after testing.

Step 3: Select Cure System

Platinum (addition) cure: Required for:

• Food-contact applications (FDA, LFGB)
• Medical applications (USP Class VI)
• Baby products
• Pharmaceutical process equipment
• Any application where extractable purity is critical

Peroxide cure: Acceptable for:

• Industrial seals and gaskets with no food or body contact
• Automotive and electrical applications where post-cure removes residues
• Cost-sensitive applications where platinum-cure premium is unjustified

When in doubt, specify platinum cure. The cost premium is 10–30% for comparable property levels, justified by cleaner extractable profile and easier certification.

Step 4: Identify Required Certifications

Match certifications to the market your product enters:

Do not over-specify certifications. A baking mold for domestic China market needs GB 4806.11, not FDA 21 CFR. An automotive spark plug boot needs OEM ASTM D2000 compliance, not USP Class VI.

Step 5: Specify Color and Appearance

For most industrial applications, color is secondary to function. For consumer products, color is a key commercial specification:

• Translucent (natural): No pigment, lowest cost, suitable for medical tubing visualization
• White: Titanium dioxide pigmented, food-grade available, most common for kitchen products
• Custom color (Pantone): Via silicone color masterbatch, food-grade pigments available
• Transparent: Specialty grade for optical or visualization applications (specify transmittance %)
• Conductive black: Carbon black loaded, for keypad membranes and anti-static applications

Step 6: Define MOQ, Lead Time, and Sample Protocol

Standard MOQ for silicone rubber compounds:

• HTV standard grade: 25 kg per grade per color
• HTV custom formulation: 50–100 kg minimum
• LSR standard grade: 10–25 kg per grade
• RTV-1: 24 cartridges per color per carton
• RTV-2 addition cure: 1 kg trial kit, 5 kg standard set

Lead time: Standard catalog grades: 3–7 business days (ex-stock). Custom formulations: 4–8 weeks. Sample requests: 5–10 business days.

Always test a sample before production commitment. Measure hardness, tensile, and elongation on your own cured specimens and compare to TDS values before placing production orders.

Contact us to get matched with the correct silicone rubber grade for your application and request supplier qualification samples.