SORTA-Clear™ 40 and RTV-5140 are both specified at Shore A40, giving them a relatively firm cured profile for transparent mold applications. At this hardness, the silicone provides useful body and resistance to deformation during casting and handling, while offering less flexibility than softer clear silicone grades. Mold geometry and demolding requirements should therefore be considered alongside hardness when selecting an A40 material.
The mixing systems are one of the clearest differences between the two materials. Smooth-On specifies a 100A:10B ratio by weight for SORTA-Clear™ 40, requiring accurate component measurement by weight. RTV-5140 uses a 1:1 ratio by weight or volume, which simplifies component proportioning for routine batches. The different mixing systems can therefore affect weighing and day-to-day preparation requirements.
Processing time also follows a different pattern. SORTA-Clear™ 40 has a published 60-minute pot life, while RTV-5140 is listed at 40–50 minutes. SORTA-Clear™ 40 therefore has the longer published working window. Cure time differs more substantially, with approximately 16 hours for SORTA-Clear™ 40 compared with 8–10 hours for RTV-5140 under the respective manufacturers’ stated conditions. This difference may be relevant when shorter mold turnaround is required.
Viscosity requires particular attention in this comparison. Smooth-On reports 35,000 cps for mixed SORTA-Clear™ 40, while MinghuiLink reports 60,000±5,000 mPa·s for Part A of RTV-5140. Because the manufacturers report these values for different material states and measurement points, they should not be treated as a strict like-for-like viscosity ranking. The published figures nevertheless indicate different processing and handling characteristics, so the appropriate mixing, pouring and air-removal procedures should follow the respective manufacturers’ technical documentation.
The published mechanical data show a consistent difference in the reported values. SORTA-Clear™ 40 reports 800 psi tensile strength, 120 pli tear strength and 400% elongation, equivalent to approximately 5.52 MPa, 21.0 N/mm and 400%, respectively. RTV-5140 reports 3.5±0.5 MPa tensile strength, 14±0.5 N/mm tear strength and 300±50% elongation. SORTA-Clear™ 40 therefore reports higher published values for all three properties. These figures should nevertheless be treated as manufacturer-published reference data rather than a direct laboratory ranking because test methods and conditions may differ.
