DOWSIL™ SH 9555 Clear and RTV-5240 are both addition-cure silicone systems for reusable mold making, but they differ in hardness and processing profile. Dow lists SH 9555 Clear at 35 Shore A, while MinghuiLink lists RTV-5240 at 40±2 Shore A. SH 9555 is therefore softer and generally more flexible, while RTV-5240 provides greater mold body and rigidity.
Transparency is also positioned differently. Dow describes SH 9555 Clear as clear to translucent, while MinghuiLink positions RTV-5240 as a transparent silicone. Neither should automatically be described as optically clear, because final mold visibility also depends on mold thickness, surface finish and trapped air.
The working-time difference is significant. SH 9555 Clear provides approximately 90 minutes, compared with 45 minutes for RTV-5240. The longer window can be useful for large or detailed molds that require more time for mixing, deaeration and controlled pouring.
Both systems use a 10:1 mix ratio, so mixing ratio is not a meaningful differentiator. Accurate weighing remains important for both products, particularly when preparing small batches.
RTV-5240 provides the faster published cure cycle, at approximately 10 hours compared with 24 hours for SH 9555 Clear. It is therefore better suited to users who prioritize shorter mold turnaround, while SH 9555 provides more processing time before curing begins.
The published mechanical data favor SH 9555 Clear. Dow lists approximately 5.8 MPa tensile strength, 20 N/mm tear strength and 440% elongation, compared with approximately 3.5 MPa, 14±0.5 N/mm and 300±50% for RTV-5240. SH 9555 therefore combines higher tensile and tear strength with greater published elongation.
These properties lead to different mold-selection priorities. SH 9555 Clear's lower hardness and higher elongation can be advantageous when the mold needs to flex during demolding, while RTV-5240's higher hardness can provide more support and dimensional stability. The appropriate choice depends on mold geometry, wall thickness and the required release path.
Viscosity should be interpreted cautiously. The current Dow documentation does not provide an equivalent numerical viscosity value for direct comparison, while MinghuiLink publishes approximately 80,000±5,000 mPa·s for RTV-5240 Part A. A direct viscosity ranking is therefore not supported by the available published data.
Both materials can be used for transparent or translucent molds, including resin and prototype applications. Dow specifically identifies polyurethane molding, prototypes, figurines and artifact reproduction for SH 9555 Clear, while RTV-5240 is positioned for transparent molds, jewelry, resin casting and high-precision parts.
For clear or translucent molds, bubble control is particularly important because trapped microbubbles can reduce visual clarity. Careful mixing, controlled pouring and vacuum deaeration where appropriate can improve the final mold appearance. Addition-cure compatibility should also be checked with unfamiliar masters, coatings and 3D-printing materials before production.
Overall, SH 9555 Clear is better aligned with users who need a softer mold, longer working time and stronger published mechanical properties. RTV-5240 is better aligned with users who prefer a firmer transparent mold and faster curing. The choice should be based on whether flexibility and processing latitude or rigidity and production turnaround are the primary requirements.