PlatSil® 73-45 vs RTV-4145 Silicone Comparison

PlatSil® 73-45 and RTV-4145 are both Shore A45 platinum-cure silicones for reusable molds and casting applications, but their published specifications show meaningful differences in component ratio, demold time and mechanical profile. PlatSil® 73-45 uses a 1A:10B mix ratio with a 40-minute pour time and approximately 16-hour demold time, while RTV-4145 uses a 1:1 mix ratio with a 35-minute working time and approximately 6-hour cure time. PlatSil® 73-45 also reports substantially higher published elongation. These differences are particularly relevant when balancing component handling, mold turnaround and demolding flexibility.

PlatSil® 73-45 and RTV-4145 occupy the same general Shore A45 mold range, giving both materials a relatively firm cured profile with more body and deformation resistance than softer silicone grades. This hardness can provide useful support during casting and handling while retaining some flexibility for demolding. Actual mold performance still depends on mold thickness, geometry and casting material.

The main operational difference is the component ratio. Polytek specifies 1A:10B by weight for PlatSil® 73-45, which requires accurate measurement by weight. RTV-4145 uses a 1:1 ratio by weight or volume, giving users a different component-measurement workflow. The mixing systems therefore differ mainly in how the components are proportioned and prepared rather than in the nominal cured hardness.

The published working windows are relatively close. PlatSil® 73-45 has a 40-minute pour time, while MinghuiLink lists a 35-minute working time for RTV-4145. The stated demold or cure times, however, differ substantially: approximately 16 hours for PlatSil® 73-45 versus approximately 6 hours for RTV-4145 under the respective manufacturers’ stated conditions. This makes mold turnaround a more significant processing difference than the working window.

Viscosity also requires careful interpretation. Polytek reports 35,000 cP for mixed PlatSil® 73-45, while MinghuiLink reports 8,500±200 mPa·s for Part A of RTV-4145. Because the manufacturers report these values for different material states and measurement points, they should not be treated as a strict like-for-like laboratory comparison. The published data nevertheless indicate different processing characteristics, so mixing, pouring and air-removal procedures should follow the respective technical documentation.

The mechanical data show a particularly large difference in reported elongation. PlatSil® 73-45 is listed at 707% elongation, compared with 230±50% for RTV-4145. Polytek also reports 631 psi tensile strength and 145 pli Die B tear strength, while RTV-4145 reports 4.7±0.5 MPa tensile strength and 30±0.5 N/mm tear strength. The tear figures are based on different reported test methods and should not be treated as a direct ranking. The published elongation values do, however, show a substantial difference that may be relevant when an A45 mold must tolerate significant stretching during demolding.