PlatSil® 73-25 and RTV-4125 are both Shore A25 platinum-cure silicones, placing them in a medium-soft range for flexible reusable molds. This hardness provides more body than very soft silicone grades while retaining substantial flexibility for many mold geometries. Actual demolding performance still depends on mold thickness, geometry and casting material in addition to Shore hardness.
The most noticeable processing difference is the available working time. Polytek specifies a 15-minute pour time for PlatSil® 73-25, whereas MinghuiLink lists a 30–40-minute working time for RTV-4125. The shorter working window of PlatSil® 73-25 requires a more prepared mixing and pouring workflow, while RTV-4125 provides more processing latitude when additional time is needed for mold preparation or air removal.
Published viscosity values are relatively close numerically, but they are reported on different bases. Polytek reports approximately 6,000 cP for mixed PlatSil® 73-25, while MinghuiLink reports approximately 4,700±200 mPa·s for Part A of RTV-4125. Because the manufacturers use different measurement points and material states, these figures should not be treated as a strict like-for-like laboratory comparison. Actual flow and air-release behavior should be evaluated with the intended mold geometry and processing method.
The published cure or demolding times are also relatively close. Polytek specifies approximately 4–5 hours for demolding PlatSil® 73-25, while MinghuiLink lists approximately 4–5 hours for RTV-4125. The similar stated turnaround means that working time is likely to be the more significant processing difference for many users. Polytek also distinguishes demolding time from the time required for the silicone to reach its final cured properties, so demolding after several hours should not automatically be interpreted as full cure.
The published mechanical data show higher reported values for RTV-4125 across the three listed properties. PlatSil® 73-25 reports 380 psi tensile strength, approximately 21.0 N/mm Die B tear strength and 405% elongation. RTV-4125 reports 4.0±0.5 MPa tensile strength, 26±0.5 N/mm tear strength and 460±50% elongation. These figures should be regarded as manufacturer-published reference data rather than a direct laboratory ranking because the manufacturers may use different test methods and conditions.
PlatSil® 73-25 also offers an additional mold-making option because Polytek documents the use of PlatThix Liquid Thickener or fumed silica to adapt the material for brush-on applications. This gives 73-25 flexibility for both pourable and buildable mold-making workflows, depending on the required mold construction method.
