Exterior trim isn’t just for show; it’s a defense against water, weather, and structural wear. In damp climates or on moisture-prone parts of a building, choosing the right trim material is important. While wood has long been the traditional choice, it’s not built to last without regular upkeep. For low-maintenance, long-lasting performance, waterproof trim materials are a smart solution.
Here are some of the most reliable waterproof exterior trim options, along with their best use cases and trade-offs.
Cellular PVC trim
Cellular PVC is one of the best-performing waterproof trim materials on the market. Made from polyvinyl chloride with a solid internal structure, it won’t absorb moisture, rot, swell, or attract insects. It’s also highly machinable, making it a popular substitute for wood in both modern and historic homes.
You can cut, mill, and install cellular PVC with standard woodworking tools. It can (and should) be painted to seal cut edges and improve long-term appearance. But this also allows you to totally customize it.
Best for: Window and door surrounds, soffits, fascia, columns, pergolas, and any application near ground contact or constant moisture. Ideal for coastal environments and high-end homes where durability and appearance matter.
Fiberglass trim
Fiberglass is another moisture-resistant material built for long-term exposure. It’s stronger than PVC, making it suitable for both structural and decorative use. It won’t rot or mold and holds up to extreme weather with minimal maintenance.
While fiberglass is exceptionally strong, it is a thin-walled material and may require special fasteners or support during installation.
Best for: Large and/or structural columns, cornices, entablatures, decorative scrolls and carved elements, and trim details that need to be both structural and decorative. Excellent for classical architecture and large-scale elements where durability is critical.
Glass fiber reinforced concrete (GFRC)
GFRC is a high-performance composite that combines a concrete matrix with embedded glass fibers. It’s completely nonporous, fire-resistant, and unaffected by freeze-thaw cycles or humidity. GFRC works well in projects where you need a premium stone or cast-concrete look, but without the weight.
Because existing trim elements can be used to cast the production molds, GFRC can replicate detailed profiles like keystones, pilasters, and historic trim—perfect for restoration or custom builds. While it’s heavier than PVC, it’s still significantly lighter than precast concrete and easier to install.
Best for: Decorative moldings, cornices, large-scale historic replications, and high-end commercial façades. One of the most durable options for non-load-bearing trim exposed to the elements
Molded polyurethane trim
Polyurethane trim is moisture-resistant, lightweight, and cost-effective, which makes it ideal for decorative applications that don’t require structural strength. It won’t warp or crack and comes pre-molded in standard profiles for brackets, cornices, and ornamental accents.
The main limitation is customization. For custom profiles, polyurethane is more cost-effective for larger production runs. The initial tooling and set-up costs for non-standard profiles can result in higher unit costs for smaller quantities (in these instances, other materials may be a better fit). That said, polyurethane is easy to install and performs well in humid environments. That said, it’s easy to install and performs well in humid environments.
Best for: Decorative brackets, corbels, and ornamental trim. Great for quick installs where durability and moisture resistance matter more than custom design.
Aluminum trim
Aluminum trim isn’t often thought of for traditional applications, but it’s naturally waterproof and corrosion-resistant, especially when factory powder-coated or coil-coated. It’s most commonly used in pergolas, trellises, and modern exterior systems where a sleek, durable finish is needed.
While it doesn’t offer the same warmth or texture as wood-based products, aluminum is a solid option for nontraditional projects that prioritize longevity and minimal maintenance.
Best for: Pergola framing, shade structures, cornices and slab-edge covers, and modern facades. Lightweight and long-lasting with a clean architectural aesthetic
Which one is right for your project?
Waterproof exterior trim is a brilliant choice when you’re working near ground level, in wet climates, or on structures that demand long-term durability with minimal maintenance. Cellular PVC is a great option across the board—it’s easy to work with, fully waterproof, and flexible enough to suit almost any design. For more specialized needs, GFRC, fiberglass, or polyurethane can be great options.
Not sure which material fits your build? Let’s connect. We’re happy to help you explore the right trim for your environment, design goals, and budget.