Silicone Rubber Buyer Guide

Silicone Rubber Buyer Guide

This guide is for procurement engineers, sourcing managers, and quality teams evaluating silicone rubber suppliers and building RFQ specifications. It covers what to specify, what certifications to demand, how to evaluate supplier documentation, and common sourcing mistakes to avoid.

Step 1: Define Your Technical Specification

Before issuing an RFQ, define the minimum technical parameters:

Product form: Which silicone type does your application require?

• HTV (mill-mixed slab/strip) — for compression molding, extrusion, calendering
• LSR (liquid two-part) — for injection molding of complex geometries
• RTV-1 (one-component cartridge) — for construction sealants and general bonding
• RTV-2 (two-component liquid) — for mold making, casting, potting

Shore hardness: Specify nominal hardness ±tolerance (e.g., Shore 50A ±5). Do not specify "soft" or "medium" without a durometer value — compound suppliers cannot quote without this.

Key mechanical properties: Minimum tensile strength (MPa), minimum elongation at break (%), minimum tear strength (kN/m), maximum compression set (%).

Temperature range: Minimum and maximum continuous service temperature. Example: "continuous service −40 °C to +180 °C."

Cure system: Specify platinum (addition) cure if the application is food-contact, medical, pharmaceutical, or baby product. For industrial applications where peroxide cure is acceptable, state "peroxide cure acceptable with post-cure."

Certifications required: List all applicable standards: FDA 21 CFR 177.2600, LFGB §30/§31, USP Class VI, ISO 10993, RoHS 2015/863, REACH SVHC declaration. Suppliers who cannot provide documentation for stated certifications should be disqualified.

Color and transparency: Specify color (RAL/Pantone if brand-controlled), opacity (transparent/translucent/opaque), and whether food-grade pigments are required.

Step 2: Evaluate Supplier Documentation

For each shortlisted supplier, request and review:

Technical Data Sheet (TDS): Must state: product form, Shore hardness, tensile strength, elongation, tear strength, operating temperature, cure system (platinum or peroxide), specific gravity. Reject TDS documents that omit the cure system — this is often a sign of unqualified product.

Declaration of Conformity (DoC): For food-contact and medical applications, the DoC must cite the specific regulation (e.g., "complies with FDA 21 CFR 177.2600, Section 177.2600(b)(1)") and be signed by an authorized representative. Generic DoCs ("this product meets all applicable regulations") are not acceptable.

Test reports: Extraction test reports (FDA or LFGB), USP Class VI biological test report, ISO 10993-5 cytotoxicity report. Reports must be from ISO/IEC 17025-accredited laboratories, issued within the past 5 years, and applicable to the compound designation you are purchasing (not a different grade).

Certificate of Analysis (CoA): Per-lot quality data including Shore hardness, tensile strength, and elongation measured on cured test specimens from the same lot. Acceptable tolerances should match the TDS values.

Step 3: Sample Testing Protocol

Before production qualification:

1. Request 200–500 g compound sample (HTV/LSR) or 2 cartridges (RTV-1) or 1 kg set (RTV-2)
2. Mold test specimens per ISO 37 (tensile dumbbell, Type 2) at your standard cure conditions
3. Measure Shore hardness (ISO 48-4), tensile strength, elongation at break (ISO 37), and tear strength (ISO 34-1)
4. Compare measured values to TDS and your specification limits
5. For food/medical grades, send sample to accredited laboratory for extraction testing or biocompatibility testing

Allow 4–6 weeks for full sample qualification including laboratory testing.

Step 4: Red Flags in Supplier Claims

Missing cure system declaration: Any food-contact or medical supplier that cannot confirm "platinum (addition) cure" in writing is a risk.

TDS with only a single property value (no range or tolerance): Legitimate TDS documents show typical values with tolerances, not single point data.

"FDA compliant" without specific CFR citation: Compliance requires a specific regulation reference (e.g., 21 CFR 177.2600), not a generic claim.

USP Class VI certificate without a test report: "Manufactured to be compliant" language without a test report is insufficient for regulatory filings.

Price significantly below market: Silicone compound market prices reflect the cost of high-purity PDMS polymer, fumed silica filler, and platinum catalyst. Prices more than 30% below comparable grades from known suppliers should trigger additional due diligence on ingredient sourcing.

Step 5: Ongoing Supplier Qualification

After initial qualification, maintain:

• Annual re-qualification testing (Shore hardness, tensile, elongation from production lot)
• Change notification agreement: supplier must notify you before any compound reformulation or raw material substitution
• Periodic audit of laboratory accreditation status for certification laboratories
• REACH SVHC candidate list updates (bi-annual) — request updated SVHC declaration from supplier each January and July

Contact us to connect with vetted silicone rubber suppliers who can provide the documentation and testing compliance your application requires.