When people think about roofing, they see rollers, resin, and membranes. They don't think about chemistry. The molecular structure of GRP and EPDM makes them tough, flexible, and resistant to weather. A bit of science shows why these two roofing systems are favored for homes, garages, and commercial roofs. The Science Behind a Strong Roof A good roof isn’t just about neat application - it’s about how the material behaves at the chemical level. Glass-reinforced plastic (GRP) and ethylene propylene diene monomer (EPDM) are made from polymers. These are long chains of molecules that provide strength and structure. How those chains form and bond determines everything from flexibility to lifespan. What Makes GRP So Durable How GRP is Made GRP stands for glass-reinforced plastic. It mixes unsaturated polyester resin with fine strands of glass fiber matting. When a catalyst is added, the resin cross-links. This chemical reaction bonds the polymer chains into one solid structure. The result is a seamless shell that hardens into a watertight, rigid surface once cured. This is great for flat roofs, balconies, and walkways. It provides strength underfoot. Why GRP Roofing Lasts Apex GRP Roofing Kits work the same way. Resin, matting, and topcoat come together to create a strong chemical bond from the inside out. GRP is different from traditional felt. It doesn’t need overlaps or joins. Instead, the chemistry forms a waterproof barrier. Understanding Polymer Behaviour To understand why GRP and EPDM behave differently, it helps to look at how their molecules are built. GRP: The Thermoset Polymer GRP is a thermoset polymer, meaning once it cures, it can’t be melted or reshaped. Its cross-linked chains form strong bonds. This makes it hard and inflexible, perfect for a durable surface. EPDM: The Thermoset Elastomer EPDM is a thermoset elastomer. It’s a type of synthetic rubber made from long, flexible carbon chains. This rubber stays elastic in both freezing and hot conditions. A cured GRP roof feels rigid and solid underfoot. An EPDM membrane flexes easily with temperature changes or building shifts. It won’t get damaged. The Flexibility of EPDM EPDM comes from synthetic rubber made of ethylene, propylene, and a bit of diene monomer. These ingredients form chains with saturated bonds. This structure fights against oxygen and ozone. These elements often lead to cracking and brittleness in other materials. That chemical stability explains why EPDM roofs can last decades with minimal maintenance. The rubber membrane remains soft and pliable even after years of UV exposure or heavy rain. Apex EPDM adhesives and accessories create a strong bond between the membrane and the deck. This forms a seamless, waterproof layer. Bonding and Adhesion Both GRP and EPDM rely on chemical bonding rather than just mechanical fixing. In GRP systems, the polyester resin bonds with the decking, trims, and matting. Once cured, it forms a single layer. That molecular grip is what gives GRP roofs their seamless finish. EPDM takes a different approach. Its contact adhesives bond at the surface. They soften both layers a bit, allowing their polymer chains to grip each other. Once the solvent flashes off, the two surfaces are locked together, flexible yet firm. Explore the bonding components and resin systems in the Apex Tools & Accessories collection. They work great with both GRP and EPDM kits. Why Weather Doesn’t Win Sun, frost and standing water are constant enemies for any flat roof. Chemistry gives GRP and EPDM their resistance. The dense network in GRP blocks water molecules. This happens even with constant exposure. EPDM's carbon backbone and protective additives stop UV damage and thermal cracking. These materials expand and contract at steady rates. This keeps them sealed around joints, trims, and edges, season after season. It’s the science of stability turned into long-term protection. Quick Comparison Material Key Chemical Trait Real-World Advantage GRP (Fibreglass) Cross-linked resin matrix Forms a rigid, seamless waterproof shell EPDM (Rubber) Long, saturated polymer chains Stays flexible and crack-resistant in all weather Both Chemical adhesion bonding Reliable seal that lasts for decades Useful Apex Roofing Resources GRP Roofing Kits – complete fibreglass roofing systems with resin, matting and topcoat. EPDM Flat Roof Systems – flexible, durable rubber membranes for long-lasting protection. Tools & Accessories – rollers, adhesives and resin systems for both GRP and EPDM applications. Apex Fibreglass Roofing Supplies – browse all roofing products, kits and materials. GRP and EPDM may look simple on the surface, but their strength lies in complex chemistry. One hardens into a solid structure; the other bends without breaking. Both rely on polymers working at a molecular level to keep your roof watertight year after year. Apex offers tough Apex GRP Roofing Kits and flexible EPDM Flat Roof Systems. The science behind these products sets them apart. Apex has everything you need to apply that knowledge in your next project.
