The short answer
Solid composite boards have a full cross-section, making them stronger, heavier and more robust — better at handling heavy loads, impacts and wider joist spacing, with a more timber-like feel and no exposed cut ends to cap. Hollow composite boards have internal voids that use less material, weigh less and cost less, and the channels can help with cable runs, but they're less strong, can feel slightly less solid underfoot, and their open ends usually need finishing trims. For heavy-use, commercial or high-traffic decks, solid is the safer choice; for budget-conscious domestic projects with proper joist support, hollow boards perform perfectly well. Both are valid — the decision comes down to load, budget and feel.
Composite boards come in two structural types — solid and hollow — and the difference affects strength, weight, cost and feel. This page compares them so you can pick the right one.
At a glance
- StrongerSolid
- LighterHollow
- CheaperHollow
- More timber-like feelSolid
- Needs end trimsHollow
What's the structural difference?
The names describe the board's cross-section. A solid composite board is filled right through — a continuous slab of wood-plastic composite. A hollow composite board has a series of internal cavities or channels running along its length, like a cross-section with circular or square holes, leaving the top, bottom and side walls connected by ribs. Removing that internal material is what makes hollow boards lighter and cheaper, because they use less composite per board. Both can be capped or uncapped and both come in the same colours and surface finishes, so structurally they look identical from above once installed — the difference is what's going on inside and how that affects strength, weight, feel and cost.
Strength, weight and feel
The structural difference has practical consequences. Solid boards are stronger and stiffer, so they handle heavy point loads, impacts and slightly wider joist spacing better, and they feel reassuringly substantial underfoot — closest to real timber. That strength suits high-traffic, commercial or heavy-use decks, and decks carrying heavy furniture or hot tubs. Hollow boards are lighter, which makes them easier to handle and transport and can speed installation, but they're less strong, so they need adequate joist support and can feel slightly less solid or sound a little more hollow when walked on. The voids also make them marginally more vulnerable at the ends if water gets in, which is why finishing the open ends matters. For ordinary domestic foot traffic with correctly spaced joists, hollow boards are perfectly serviceable; for heavy or demanding use, solid has the edge.
Solid vs hollow side by side
The table is a broad guide; exact figures vary by brand and product.
| Factor | Solid composite | Hollow composite |
|---|---|---|
| Strength / load | Higher | Lower |
| Weight | Heavier | Lighter |
| Relative cost | Higher | Lower |
| Feel underfoot | Solid, timber-like | Slightly less solid |
| Cut ends | Clean, no trim needed | Open, usually need trims |
| Best for | Heavy/commercial use | Budget domestic decks |
Indicative comparison for guidance only. Sources: composite decking manufacturer specifications.
Finishing, cost and installation
Two practical points often decide it. First, cost: hollow boards use less material, so they're generally cheaper per square metre, which can be a meaningful saving across a large deck — part of why they're popular for budget-conscious domestic projects. Second, finishing the ends: a hollow board has open cavities at its cut ends, which look unfinished and can let in water and debris if left exposed, so they usually need end caps or fascia/trim boards to close them off neatly. Solid boards have a clean cut end that needs no such treatment, simplifying edges and steps. Installation otherwise is similar, but the hollow board's lower weight makes handling easier, while its lower strength means you must follow the manufacturer's recommended joist spacing closely — under-supporting a hollow board is where problems like flex or sagging arise.
Durability and longevity over time
Both board types can last well, but their structure affects how they age. Solid boards have no internal voids for water or debris to collect in, so once installed they're a little more forgiving of less-than-perfect conditions and resist the slow ingress that can affect a poorly finished hollow board. Their greater mass and stiffness also means they flex less over years of foot traffic and furniture, holding a flat, stable surface for longer. Hollow boards are perfectly durable too, provided two things are right: the open ends are properly capped or trimmed so water and dirt can't sit in the cavities, and the joist spacing follows the maker's spec so the board isn't asked to span further than it's designed to. Where those are neglected, a hollow board is more likely to develop flex, trapped moisture or end damage over time. With both types, the cap quality remains the biggest single factor in how well the surface resists fading and staining across a 20–30 year life — structure decides strength and feel, but the cap decides how it looks years on.
Which should you choose
Choose solid composite if you want maximum strength and durability, the most timber-like feel, clean exposed ends with no trims, or you're building a high-traffic, commercial or heavy-load deck (furniture-heavy areas, hot tubs). Choose hollow composite if budget matters, you want lighter boards that are easier to handle, and your deck is a normal domestic one with properly spaced joists — in which case it performs well for less money. Many homeowners are happy with quality hollow boards; many specifiers prefer solid for demanding settings. If you're genuinely unsure, it's worth handling a sample of each — the difference in weight and the feel underfoot is obvious in the hand, and often settles the decision quickly once you can compare them directly. As a rough rule of thumb, a typical family garden deck used for ordinary foot traffic and some furniture is well served by quality hollow boards on correctly spaced joists, while anything carrying concentrated heavy loads, a hot tub, or constant high traffic leans towards solid for the extra strength and reassurance. Whichever you pick, the cap quality, joist support and installation matter as much as solid-versus-hollow to how the finished deck looks and lasts.
Frequently asked questions
Are solid or hollow composite decking boards better?
Neither is universally better — it depends on use and budget. Solid boards are stronger, more durable and feel more like timber, suiting heavy or commercial decks, while hollow boards are lighter and cheaper and perform well on normal domestic decks with proper joist support. Match the board to your loading, budget and the feel you want.
Do hollow composite boards need end caps?
Usually yes. Hollow boards have open cavities at their cut ends that look unfinished and can let in water and debris, so they're normally finished with end caps or fascia and trim boards to close them off neatly. Solid boards have a clean cut end and don't need this treatment, simplifying edges and steps.
Do hollow composite boards sound hollow when you walk on them?
They can feel and sound slightly less solid than solid boards underfoot, particularly if joist spacing is too wide. Following the manufacturer's recommended joist centres and fixing them down properly minimises this. Solid boards give the most substantial, timber-like feel, which is one reason they're preferred for high-traffic decks.
Sources & further reading
Figures on this page are typical UK ranges drawn from published sources and depend on your specific garden. They are guidance, not a quotation.