What is a Composite Door Made Of?

Uncover the layers of material that make composite doors strong, secure, and stylish. From the robust core to the weatherproof skin, explore what goes into manufacturing a product that will reliably protect your home for years. Let’s find out how a composite door is made.

The Anatomy of a Composite Door

Composite doors have surged in popularity recently as an attractive and high-performance alternative to traditional wooden or basic uPVC doors. But what exactly is a composite door made from? Let’s peel back the layers and look at the components and materials that comprise a typical composite door.

A solid, high-density core is at the heart of a composite door. It provides the bulk of the door’s strength, soundproofing, and insulating properties. This core is usually made from solid wood or an engineered wood product that combines fine wood particles with synthetic polymers like plywood.

The wood fibres, often derived from fast-growing, sustainably harvested softwoods like spruce or pine, are dried and mixed with a resin binder and sometimes other additives. This mixture is subjected to heat and pressure to form a dense, uniform substrate with excellent structural stability and moisture resistance.

Surrounding this wooden core are two thinner layers, or “skins,” that create the door’s smooth, durable exterior surface. These door skins are most commonly made from glass-reinforced plastic (GRP), a rigid composite material comprising a polymer resin matrix interlaced with fine glass fibres for added strength.

During manufacturing, the GRP is moulded and bonded directly to the core under high pressure, yielding a laminated composite over the sum of its parts.

GRP is an ideal skin material for several reasons. The glass fibre reinforcement gives it an exceptional strength-to-weight ratio, allowing for a relatively thin door skin that doesn’t compromise the door’s integrity. GRP is highly resistant to weathering, UV radiation, and corrosion, meaning the door’s surface won’t warp, crack, or fade over time like wood might. It also has a low thermal conductivity, boosting the door’s insulating performance.

What’s more, GRP is impressively customisable from an aesthetic standpoint. The material can be pigmented and textured to mimic the look of wood grain, complete with knots and grooves, so closely that it’s hard to discern from the real thing.

Alternatively, composite doors can be finished in a wide range of solid colours or other decorative designs to suit different architectural styles and personal tastes. This versatility is a significant selling point for composite doors.

In addition to the wood core and GRP skins, composite doors incorporate several other materials to enhance their all-round performance:

• Polyurethane (PU) foam: This is sometimes injected into the core during manufacturing to provide an extra layer of thermal insulation. PU foam helps composite doors achieve excellent U-values (a measure of heat transfer), making them highly energy-efficient.
• EPDM rubber seals: Ethylene propylene diene monomer (EPDM) is a synthetic rubber for weather-stripping seals around composite door edges. EPDM maintains flexibility and resilience in hot and cold conditions, ensuring a weathertight, draught-excluding fit in the doorframe year-round.
• uPVC frame: The door is made of wood/GRP composite construction, and it’s typically mounted in an unplasticised polyvinyl chloride (uPVC) frame. This low-maintenance, insulating plastic provides a stable foundation and an additional weather barrier for the door. The frame usually contains multiple chambers that enhance its rigidity and thermal efficiency.

Components like hinges, handles, locks, and glazing panels are added to create a complete door system. Composite doors often utilise multipoint locking mechanisms with steel hooks, bolts, and cylinders for optimal security. Double- or triple-glazed glass panels may be included to allow light in while still providing insulation and protection.

So, in summary, the primary materials found in a composite door are:

• Wooden core
• Glass-reinforced plastic (GRP) exterior skins
• Polyurethane (PU) foam insulation
• Steel or aluminium reinforcement
• EPDM rubber seals
• uPVC frame

Together, these disparate elements are engineered into a high-performance composite that offers the best characteristics of its constituent materials. The result is a more robust, secure, and thermally efficient door than traditional timber doors, with a more natural and convincing woodgrain effect than plain uPVC doors.

The specific composition of a composite door may vary somewhat between manufacturers, who may use proprietary materials or construction techniques to differentiate their products. However, composite doors’ general makeup and benefits are consistent across the board.

It’s worth noting that while composite doors are often referred to as “GRP doors,” this isn’t entirely accurate. GRP (glass-reinforced plastic) refers only to the door’s outer skins, not the composite construction. A proper composite door will always have a high-density core (usually wood/plywood) and GRP facings.

When shopping for a composite door, it’s a good idea to inquire about the specific materials and manufacturing processes used, as these can affect the door’s quality, durability, and performance. Look for doors tested and certified to recognised standards such as PAS 24 for enhanced security and Document Q for building regulation compliance.

High-quality composite doors may cost more upfront, but their longevity and superior insulation can make them a worthwhile investment in the long run.

In conclusion, composite doors are a marvel of modern materials science, combining the best attributes of natural wood, glass-reinforced plastics, and advanced insulating foams to create a door built to last. By understanding what goes into a composite door, homeowners can better appreciate the benefits these doors offer in terms of strength, security, style, and sustainability.

While no door is entirely impervious to wear and tear, a well-made composite door is designed to withstand the elements and provide reliable performance for many years with minimal maintenance required. As composite door technology continues to evolve, we expect to see even more exciting innovations in materials and design that will take this 21st-century door solution to new heights.