High-Temperature Vulcanizing (HTV) or Heat Cured Rubber (HCR) is the backbone of durable silicone manufacturing. Used in everything from automotive gaskets to medical tubing, selecting the right grade requires a rigorous evaluation of its processing behavior and final physical properties.

1. Raw Material Characteristics
Before vulcanization, the physical state of the gum dictates how it will behave in the mixer or extruder.

- **Viscosity & Mooney Viscosity:** Determines flow characteristics. High viscosity materials may require more energy to process but often offer better green strength (handling strength before curing).
- **Plasticity:** Essential for compression molding. The material must flow into the mold cavity without being so fluid that it creates excessive flash.
- **Structure:** Check if the gum is "structured" (highly viscous, requires breakdown) or "pumpable" (for liquid injection systems).

2. Curing Parameters
- **Cure Rate:** Evaluated using a Rheometer. It is vital to know the $T_{90}$ (time to 90% cure) to optimize cycle times.
- **Scorch Safety:** The material must not begin to cure prematurely during mixing or storage.
- **Post-Cure Requirements:** HTV silicones often require a secondary oven cycle (e.g., 4 hours at 200°C) to reach optimal physical properties and burn off volatiles.

3. Mechanical Performance
- **Tensile Strength & Elongation:** Measures the force required to break the material and how much it stretches. High tear strength is critical for demolding complex parts.
- **Compression Set:** The ability of the rubber to return to its original thickness after being compressed. Low compression set is non-negotiable for sealing applications.
- **Hardness (Shore A):** Verified to ensure the rubber meets the specific durometer requirements (e.g., 40A vs. 70A).

4. Additives & Certification
- **Reinforcement:** Presence of fumed silica for strength.
- **Colorability:** Ability to accept pigments without affecting cure.
- **Compliance:** Verification of FDA, USP Class VI, or UL94 V-0 (flame retardancy) standards.

Summary
A comprehensive checklist for HTV/HCR ensures that the silicone gum not only processes efficiently but delivers the resilience and thermal stability required for its end-use application