Concrete molds place very different demands on silicone than small decorative casting projects. The mold often has to handle heavier materials, larger cavity sizes, and repeated demolding without losing shape or tearing around edges, corners, or deeper details.
For concrete applications, the key is not just flexibility. The silicone also needs enough body to support the mold structure, enough tear resistance to handle repeated use, and enough durability to perform well in larger molds such as planters, statues, letters, and custom architectural pieces.