Hollow vs solid composite decking boards: weight, feel and where each belongs

Stand a hollow board and a solid board on end and the difference is obvious. One has a row of chambers running its full length, and the other is composite all the way through. In one Australian maker's hollow and solid boards, the chambers take out about a quarter of the weight. They also shorten how far the board can span, and they leave open ends you have to cover. The longer warranty sits on the solid board, so know what you're giving up before you choose hollow.

Composite decking hollow vs solid: what you can feel

Weight is the first thing. In one Australian maker's range sold in both profiles at the same size, the hollow board is listed at 15.1 kg per 5.4 m length¹ and the solid one at 20.3 kg⁴. Over a deck of fifty boards that's about a quarter of a tonne less to carry up the side of the house. If you're doing the job alone, or the deck is on a balcony or a rooftop with a load limit, that matters.

Stiffness comes next. That maker says its hollow-core boards need a closer residential span because they're hollow³, and Trex's UK site says hollow boards aren't as durable as the dense core of a solid board⁷. None of the makers' documents cited here says how a hollow board sounds or feels underfoot, so I'd stand on a sample of each before choosing.

The open ends

Cut a hollow board and you're looking into the chambers. Trex's UK site says hollow boards give a deck "a more manufactured, less organic look", most obvious in the holes at the board ends, and sells finishing strips as an add-on to cover them⁷. The Australian hollow range I checked has no matching edge boards at all¹, and its manual has you cut a fascia board and a decking board together to make your own edge².

A picture-frame border to hide the ends needs extra noggins in the frame, as the same manual's finishing diagrams show. Budget for it before you price the boards, because a cheap hollow deck with an expensive border isn't cheap any more. On a picture-framed deck the field boards' ends are hidden anyway, so there the open ends stop mattering. Picture-frame borders on a composite deck covers the framing.

Water is the other thing I'd think about. Both of that maker's manuals say board ends near pools or spas, or anywhere with constant moisture, must be sealed with a clear solvent-based sealer². A hollow board has more open end to deal with, so on a low deck or beside a pool I'd cover the ends as well as seal them. Composite decking around pools has the rest of the pool detail.

Spans, joists and bounce

In the range I could compare, the hollow board needs closer joists than the solid one of the same section. The hollow board is rated for 400 mm centres on a house deck and 350 mm on stairs or commercial decks², while the solid board from the same maker allows 450 mm on a house deck⁴. So the hollow deck needs more joists under the same area. Price the frame and the boards together.

On Whirlpool in August 2026, Benmc was building a low deck with hollow-core boards and had found advice ranging from 300 mm to 450 mm centres, with some timber already delivered for the 420 mm he'd planned¹⁰. TSQ backed the closer figure and added that "Composite I've seen does become more flexible under summer sun"¹⁰. A month later Benmc reported going with 400 mm centres¹⁰. I'd take that warning seriously with a hollow board, which has less material in it to resist sag. Use the maker's figure for the board you're buying and don't round it up. The joist spacing guide covers why the number is a maximum.

Heavy point loads are the other limit. Trex's UK site recommends solid boards where the deck has to carry something heavy, such as a hot tub⁷. If you're thinking of a spa, I'd go solid and have the frame under it designed for the load.

Heat, fade and scratches

None of the makers' documents cited here gives a figure on whether hollow boards run cooler. A Whirlpool poster said in 2015 that hollow composites "have better heat minimisation"⁹, but the hollow range I checked says only that its boards get marginally hotter than timber and that darker colours absorb more heat³. Colour is the thing I'd choose on, and does composite decking get hot covers it.

Fade and scratches follow the cap more than the core. In the Australian range sold both ways, the hollow and solid boards share the same capping³, so I'd expect them to fade and scratch alike. Trex's UK site goes further and says hollow boards, being lower-budget, are more prone to fading and staining than solid ones, and more susceptible to mould⁷. That's a maker of solid boards talking, so I'd weigh it against the hollow board's own cap and warranty. The hollow range I checked carries a 10-year warranty¹, while the solid range from the same maker carries 25 years for a house deck⁴. The longer promise sits with the solid board.

What owners say

The forum posts cited here lean solid. On Whirlpool in 2014, dejainc put it in one line: "I wouldn't get the hollow stuff, only solid"⁹. Another poster in the same thread made a point of saying their deck was solid boards, not hollow, and the person asking the question decided that afternoon to avoid hollow. In 2024 resolve03 had samples from six brands and could see little difference between them apart from one brand's board being hollow, which they counted against it even though that brand had the colour they wanted¹¹.

Those posts are short and some are old. The hollow range I checked is capped like its solid sibling, and it's still the lighter board with the shorter warranty.

Widths and lengths sold in Australia

The solid board I compared is 137 mm wide and 23 mm thick, in 5.4 m lengths⁴. One maker also sells a narrow board 88 mm wide in the same thickness and length⁵, and another lists decking boards from 126 mm to 200 mm wide, 32 mm thick and 3.6 m long⁶. A Whirlpool poster wrote in 2024 that the eBay seller who supplied the boards for their two decks imported 5.8 m lengths to fit the shipping container, when everyone else sold 5.4 m¹¹. The hollow board I checked comes in the same 137 by 23 section¹ and fixes with the same clip system as its solid sibling, with a choice of 3 mm or 6 mm gaps⁴.

Between hollow and solid sits the scalloped board. One American maker sells its entry-level line that way and calls it its lightest composite board⁸. Check its spans and how its ends are finished in the maker's guide, as you would for any board.

Before you order

If the deck is under a roof or you're carrying every board yourself, hollow is a reasonable choice. Plan the border or fascia that hides the ends, and price the extra joists. If the deck will carry a spa or heavy planters, or you plan to own the house for twenty years, I'd buy solid for the stiffer board and the longer warranty. Either way, order a sample of each, stand on it over two bricks spaced at the joist centres you're planning, and see how each one feels. What is composite decking covers the basics, and the capped vs uncapped guide covers the other half of the decision. Once you've chosen, the board calculator will count what you need.