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What is composite?

The Wood Guide · Choosing and comparing

Material

What is composite?

A material made of two parts that together can do more than either can alone. In the garden it usually means one specific kind: composite decking boards.

  • Matrix plus reinforcement
  • In the garden: WPC
  • Wood fibre in plastic
composite material
Composite decking boards: hollow chambers and a grooved surface
Composite decking boards: hollow chambers and a grooved surface
Composite colour samples with an embossed wood grain
Composite colour samples with an embossed wood grain
Summary

Composite at a glance

A composite material made up of a matrix and a reinforcement — two components, each with its own job.

The matrix — often a polymer, sometimes metal or ceramic — binds the reinforcement together, spreads the load and protects against the environment. The reinforcement — fibres or particles — provides strength and stiffness. Together they deliver properties that neither has on its own.

In the garden it is almost always about one specific composite: WPC, wood plastic composite. Wood fibre or wood flour mixed with polyethylene or polypropylene, pressed into decking boards and cladding.

Why wood fibre in plastic

Pure plastic boards expand a lot in the sun and feel cheap. Adding wood fibre makes them stiffer and more stable and gives them a matt, more wood-like surface. The wood-fibre share is usually between fifty and seventy per cent — and that share determines the character.

Structure
matrix (binds and protects) plus reinforcement (strength)
In the garden
WPC: wood fibre in polyethylene or polypropylene
Wood share
usually 50 to 70%
Maintenance
no oil or stain needed
Service life
usually 15 to 25 years
Weak point
heat, expansion and scratches

To be fair: composite gets hot. Dark boards in full sun can become so warm that you cannot stand on them barefoot — noticeably warmer than wood, which conducts heat less well. It also expands more than wood along its length, so generous gaps at the ends are essential, and scratches cannot be sanded out the way they can with wood.

In pictures · composite or wood, an honest comparison1 / 9
What composite is

Matrix plus reinforcement

The matrix binds the reinforcement together, spreads the load and protects against the environment. The reinforcement — fibres or particles — provides strength and stiffness. Together they can do more than either can alone.

Click a chapter or use the arrows · heat and expansion drawn qualitatively, not to scale.

Beyond the garden

Where else you find composites

Type Matrix Reinforcement Use
WPC Polyethylene or polypropylene Wood fibre or wood flour Decking boards, cladding
Glass-fibre reinforced plastic Polyester or epoxy Glass fibre Boats, roofs, panels
Carbon-fibre composite Epoxy Carbon fibre Aviation, sport, bicycles
Sandwich construction Two stiff skins Light core (balsa, foam) Wind-turbine blades, aircraft panels
Reinforced concrete Concrete Steel Construction — the oldest mass composite
Wood is a composite too

Botanically, wood is exactly what the definition describes: cellulose fibres embedded in a matrix of lignin. What industry imitates with fibre and polymer, a tree has been doing for millions of years — and with a better repair trick, because wood grows.

For the deck

The honest comparison

Composite

Wins on

  • No oiling, staining or sanding — ever
  • No splinters, pleasant for bare feet and children
  • Even colour that does not turn grey
  • Stable across the width; no cupping
  • Often made from recycled material
Wood

Wins on

  • Stays cooler in full sun
  • Scratches and worn patches can be sanded out
  • Ages with character instead of turning dull
  • Completely natural and simply biomass at the end of its life
  • Lower purchase cost for most species
What the brochures don't say

"Maintenance-free" does not mean "stays looking new". Composite also greys and dulls, only more slowly and irreversibly — you cannot sand it back like wood. And composite gets green algae just the same; you still have to brush it off.

Deciding

Which material for your deck

Choose composite if

You really don't want to do any maintenance, children run around barefoot and you want an even colour that stays the same for years. Do choose a light shade to limit the heat.

Choose wood if

Your deck will be in full sun, you value a natural material that ages, or you want to be able to sand out scratches and worn patches later.

With composite, check

Solid or hollow profile — hollow is cheaper and lighter but less strong. Ask about the expansion gaps at the board ends; with composite they are larger than with wood.

With wood, check

The durability class and whether the boards are kiln-dried. See best wood species for decking.

Our choice

We work with solid wood. Not because composite is bad, but because it is a different trade: buying, drying, sawing and building with wood is what we do. This page is in the register because you deserve an honest comparison, even when it does not come out in our favour.

Quick answer

Frequently asked questions about composite

What exactly is composite?

A composite material made of a matrix (which binds and protects) and a reinforcement (which provides strength). In the garden it usually means WPC: wood fibre in polyethylene or polypropylene.

Is composite better than wood for a deck?

Not better, different. Composite needs no maintenance and does not splinter; wood stays cooler in the sun, can be repaired by sanding and ages with character.

Does composite get hot in the sun?

Yes, noticeably hotter than wood — especially dark colours. Wood conducts heat less well and so feels cooler. Choose a light shade if the deck is in full sun.

Can I remove scratches from composite?

Hardly. Where you can sand a scratch out of wood and refinish it, the colour of composite runs right through the material and sanding is rarely a solution.

More in The Wood Guide

Composite in perspective

Two materials that together can do something neither can alone — which, incidentally, wood already does by itself.

Best wood for decking Building a wooden deck To The Wood Guide

Have a question about your project? Just ask — we're happy to help.

Photos via Wikimedia Commons: Composite decking boards: hollow chambers and a grooved surface — Geolam, CC BY-SA 3.0 · Composite colour samples with an embossed wood grain — VarunRajendran, CC BY-SA 3.0

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