Hollow vs Solid Composite Decking Boards — Which Is Better?

When you start shopping for composite decking, you'll quickly notice that boards come in two structural types: hollow and solid. Both are composite — meaning they contain wood fibre and plastic — but they differ significantly in their construction and their best applications.

Here's everything you need to know to make the right choice.

What Is Hollow Composite Decking?

Hollow composite boards have a series of internal voids running through their length. Think of it a bit like a double-skin construction — solid outer walls with empty chambers inside.

This construction makes hollow boards:

• Lighter — easier to handle and transport
• Less expensive — less material per board
• Faster to heat and cool — the hollow chambers allow less heat storage
• Slightly less rigid over long spans

Hollow boards are the most common type in the residential UK market, representing the majority of composite decking sold for domestic gardens.

What Is Solid Composite Decking?

Solid composite boards are exactly that — fully solid core with no internal voids. This construction makes them:

• Heavier — noticeably so when handling large boards
• Stronger — better load capacity and greater rigidity over longer spans
• More expensive — more material per metre
• Better for commercial or high-traffic applications

Solid boards are often specified for commercial settings, public spaces, and decking adjacent to pools where the additional structural rigidity and resistance to point loads is valued.

Structural Performance

For most domestic garden decks, hollow boards perform perfectly adequately. Standard joist spacing of 400mm centres provides sufficient support for hollow boards in normal residential use — foot traffic, garden furniture, and the occasional heavy potted plant are all within specification.

Where solid boards make more sense:

• Spans greater than 400mm between joists — solid boards are more forgiving of wider joist spacing
• Very heavy loading (hot tubs, large planters, commercial furniture)
• Steps and high-traffic areas where point loads are more concentrated

For a standard domestic patio deck used for typical garden activities, hollow boards are the appropriate choice and represent better value.

Heat Retention

This is one of the less obvious differences between hollow and solid boards. Solid composite boards retain heat more effectively — which means they can become uncomfortably hot underfoot on very sunny days, particularly in darker colours.

Hollow boards, with their air-filled chambers, heat up faster but also dissipate heat more quickly. For south-facing decks in UK summers (which can produce surprisingly high surface temperatures on dark composite), hollow boards are generally more comfortable underfoot.

Cost

Hollow composite boards are consistently cheaper than solid equivalents in the same product range. For a standard domestic deck, the cost difference across the whole project can be significant.

Browse our grey composite decking, black composite decking, and teak composite decking for current pricing.

Cut Ends and Capping

One practical consideration with hollow boards: when you cut them, the hollow internal structure is exposed. This cut end needs to be capped with a composite end cap or a fascia board to prevent debris and moisture accumulating inside the board. Most composite decking systems include compatible end caps.

Solid boards don't have this issue — the cut end is simply a flat, solid face.

The Verdict

For most domestic garden decks: Hollow composite boards are the right choice. They're lighter, less expensive, and perform excellently for residential applications.

For commercial, high-traffic, or heavy-loading applications: Consider solid composite boards for the additional structural performance.

Regardless of which type you choose, the subframe specification matters as much as the board type. A hollow board on a well-built, correctly spaced subframe will outperform a solid board on a poorly built frame. See our composite decking installation guide for correct subframe specification.