Capped vs uncapped, hollow vs solid: composite decking types explained

Composite decking prices run from £25 a board to over £80, and the difference is almost never the colour. It is the construction: whether the board is hollow or solid, whether it has a protective cap, and what the core is made of. This guide explains the four decisions in plain terms, says where our boards sit, and tells you honestly when it is worth paying more.

The short answer

Most composite decking sold in the UK is uncapped, hollow-core WPC (wood-plastic composite) at £25 to £40 a board, and it is a good product for a domestic garden if it is fitted properly. Capped boards add a plastic shell that resists stains and fading better, for roughly double the price. Solid boards are heavier and stiffer, useful for commercial decks and hot tubs. Our boards are uncapped, hollow, reversible WPC at £25 for 3.6m and £34 for 4.8m; the rest of this guide explains what that means and what you would gain by spending more.

1. Hollow or solid core

Hollow boards have channels running through them, like a Aero bar. They are lighter, which makes them easier to carry and fit, and cheaper, because there is less material. They need their cut ends capped or hidden so water does not sit in the channels, and they need joists at 350mm centres or closer because they flex more than solid boards.

Solid boards are the same material all the way through. They weigh roughly twice as much, feel more like timber underfoot, can be cut and left exposed at the end, and take heavier point loads. They cost 40 to 80% more and are harder work to lay.

Which to choose. Hollow for almost every domestic deck. Solid if the deck will carry a hot tub, if it is a commercial or public space, or if you want the heaviest, most timber-like feel and the budget allows. Ours are hollow; the installation guide gives the joist centres and end-capping that make hollow boards last.

2. Capped or uncapped

Uncapped boards are the composite mix through and through. The wood fibre is exposed at the surface, which gives a natural matt woodgrain look, and it is what makes the board lighten slightly in its first few months as the tannins react with light. Uncapped boards can take a stain if grease is left on them, and they need a wash twice a year in a shaded garden.

Capped boards have a thin shell of polymer bonded around the core, on three or four sides. The cap resists stains, holds colour with less initial shift, and shrugs off algae more easily. It gives a slightly glossier, more uniform look that some people find less like wood. Capped boards typically cost £50 to £80 for a 3.6m length.

Which to choose. Uncapped if you want the most natural finish at the lowest price and are happy to sweep and wash the deck twice a year. Capped if the deck is under trees, gets a lot of barbecue use, or you want the colour to stay as close to day one as possible and the budget stretches. Our boards are uncapped; the colour guide explains the settling you should expect.

3. What the core is made of

WPC (wood-plastic composite) is the standard: roughly half recycled wood fibre and half recycled polyethylene or PVC, pressed with pigment and UV stabiliser. It looks and feels closest to wood, and it is what we sell.

Mineral or rice-husk composites replace the wood fibre with a mineral filler or rice husk. They absorb less water and move less with temperature, and they cost more. Some premium UK brands use them.

PVC decking has no wood at all. It is the lightest, most stain-proof and most expensive, and it looks the least like timber. It is common in the US and rare in UK gardens.

Which to choose. WPC for a normal garden deck. Mineral or PVC if you are building over water, in a very exposed coastal spot, or want zero maintenance and can pay for it.

4. Surface and reversibility

Boards come with a grooved face, a woodgrain embossed face, or a brushed finish. Grooves give the most grip and hide scratches; woodgrain looks most like timber; brushed gives a soft matt texture.

Our boards are reversible, with grooves on one side and an embossed woodgrain on the other, so you choose the face when you lay them and can mix them for a border. Both faces are textured for grip when wet. Single-sided boards are usually solid or capped and the extra cost buys the finish, not the option.

What the money buys, side by side

	Uncapped hollow WPC (ours)	Capped hollow WPC	Capped solid or mineral
Price per 3.6m board	£25	£45 to £65	£65 to £90
Price per m², boards only	about £46	£85 to £120	£120 to £170
Weight per board	light, one person	light to medium	heavy, two people
Colour in the first six months	lightens slightly, then holds	minimal shift	minimal shift
Stain resistance	wipe grease the same day	high	high
Cleaning	sweep, wash twice a year	sweep, wash yearly	sweep, wash yearly
Cut ends	cap or hide	cap or hide	can be left
Joist centres	350mm max	350 to 400mm	400 to 450mm
Hot tub or heavy point loads	with a reinforced frame	with a reinforced frame	yes
Warranty, typical	10 years	15 to 25 years	25 years

Is the premium worth it?

On a 15m² deck, the boards are about £750 in our range, £1,500 for a capped equivalent, and £2,200 for capped solid. The frame, clips, trims and labour cost the same in all three cases. So the question is whether stain resistance and a longer warranty are worth £750 to £1,450 to you.

For a family garden deck used for sitting, eating and children, in our honest view, usually not. An uncapped hollow board fitted properly and washed twice a year lasts well past its warranty and looks like wood doing it. For a deck under a dense tree canopy, a rental where nobody will wash it, a commercial site, or a hot tub platform, the extra money is well spent.

What to check on any board, whoever sells it

• Dimensions. 150mm × 25mm is the standard. Thinner boards need closer joists.
• Recycled content. Ours are recycled wood fibre and recycled plastic. Virgin plastic boards are not better; they are just less sustainable.
• UV stabiliser. Ask; it is what stops the colour going chalky after year two. Ours is in the mix and covered by the 10 year warranty.
• Matching accessories. A range with fascia, L-trim, step edge and end caps in the same finish makes a finished deck; one without leaves you improvising. Ours has all four.
• Samples. Any supplier who will not send a free sample is telling you something.

Order free decking samples, leave them outside for a week, stand on them wet and dry. If you want to compare with a capped board, put one next to ours and judge whether the difference is worth the price. The cost guide prices the whole deck, and the problems guide covers what to watch for once it is down.