Does Millboard Decking Get Hot in the Sun?

Yes, Millboard decking can become hot when exposed to strong direct sunlight, particularly darker colours. That's normal for outdoor surfaces and it's worth considering when you're designing a sunny garden, south-facing terrace, balcony or roof terrace. However Millboard shouldn't simply be treated as another conventional wood-plastic composite board. Its construction is different, and factors like colour, how long the sun hits it, garden orientation, surrounding buildings, shade and how you'll actually use the deck all change how warm the surface feels.

Millboard themselves say darker boards can become hot in direct sunlight and they recommend considering footwear on particularly hot days. They also advise caution around reflective glass that can intensify heat build-up. So if you're looking at Millboard for a sunny space, the better question isn't just does Millboard get hot — it's which Millboard colour and deck design makes sense for the way your garden gets sun.

What Millboard Is Actually Made From

This matters because Millboard often gets lumped in as composite decking and people assume it's built the same way as standard WPC. It isn't.

Current Enhanced Grain is described by Millboard as a polyurethane resin and mineral composite, RMC, and they state it's 100% wood-free. Traditional WPC generally mixes wood fibres or flour with polymers. Millboard uses a different material construction and a different manufacturing process — boards are moulded from real oak masters and hand-coloured to get that variation of natural timber.

So when we compare heat, expansion, appearance or maintenance, we always compare specific products, not just assume every material marketed as composite behaves the same.

Why Any Decking Gets Hot — And What Changes It

Any external surface absorbs energy from sunlight. Decking, porcelain paving, stone, artificial grass, metal, timber and composite can all become warmer than the air temperature when they're in direct sun.

How hot a Millboard deck feels depends on board colour, intensity of sunlight, how long it's exposed, time of day, air temperature, wind and ventilation, surrounding walls, nearby glazing, garden orientation and available shade. That means the same Millboard colour can feel very different in two gardens. A partially shaded garden with mature planting around it isn't comparable to an exposed south-facing roof terrace that gets sun for most of the day. We've stood on the same colour in two different gardens on the same afternoon and had completely different impressions.

Do Dark Millboard Colours Get Hotter?

Colour makes a big difference. Millboard specifically notes in their care guidance that, like other surfaces, darker boards can get hot under direct sunlight. That's the general principle — darker surfaces tend to absorb more solar energy than lighter ones.

Their range goes from lighter natural tones through to much darker finishes. Enhanced Grain for example includes lighter options like Limed Oak and much darker options like Ebony Grey. That doesn't mean you should automatically avoid dark. A dark deck can look fantastic against contemporary architecture, dark aluminium doors, rendered walls and modern planting.

Instead ask how the space will actually be used. If the deck gets strong sun for hours and kids regularly run around barefoot on it, temperature carries more weight. If it's mainly an evening dining terrace that only gets late sun, a darker colour is far less of a practical issue.

South-Facing Gardens And Which Colour Makes Sense

Yes, Millboard can be used in south-facing gardens. A south-facing aspect doesn't make it unsuitable — it just makes sun exposure an important part of choosing colour and designing the space.

Before choosing, we always tell clients to look at where the deck will sit, how long that spot gets direct sun, whether it's morning or afternoon sun, existing trees and planting, shadows from the house, neighbouring buildings, any planned pergola or shade, and whether people will regularly walk barefoot there. Two south-facing gardens can have completely different exposure because of their surroundings.

South-east and south-west are worth thinking about too. South-east tends to get stronger sun earlier in the day, south-west gets substantial afternoon and evening sun which often lines up with when people actually use their seating and dining areas. If the deck will sit right outside large rear doors, it's worth watching that area through a sunny day before final colour decision, particularly in spring and summer when the sun's path shows you how the finished space will perform when you use it most.

There is no single best colour for every sunny garden. If keeping heat down is a priority, lighter colours are worth considering, but colour shouldn't be based on temperature alone. It needs to work with brickwork, render, window and door frames, garden furniture, paving, planting, boundaries, cladding and the style of the house. The goal is to balance practical performance with overall design. Lighter oak tones can feel bright and natural, deeper browns and greys create stronger contrast against contemporary buildings.

As Approved Millboard Installers we always recommend looking at actual board samples in the intended location rather than choosing from photos or a screen. Place physical samples where the decking will be installed, leave them during a sunny spell and compare at different times of day. Touch them. It won't be a lab test but it gives you a much better understanding of real conditions at your property than looking at samples indoors. Natural daylight makes a board look quite different from showroom photography.

Bare Feet, Comparisons With Composite And Timber, And Movement In Heat

Under strong direct sunlight a dark outdoor surface can become uncomfortable to walk on barefoot. Millboard's summer care advice acknowledges that and suggests considering footwear during hot conditions. That's particularly worth thinking about for family gardens, children's play areas, hot tub surrounds, poolside areas, exposed balconies and roof terraces. Rather than promising a product will always stay comfortable for bare feet, we think it's better to look at actual conditions of the project.

We wouldn't make a blanket statement that Millboard is always cooler than conventional composite. Composite describes a huge range of products with different compositions, colours and surface technologies, and comparing a light Millboard against a dark WPC doesn't tell you how two similar colours would compare. If heat is an important factor, compare the specific Millboard colour against the specific alternative you're considering. We cover the wider differences in Millboard vs Composite Decking: What's the Difference?

Same principle applies with timber. Natural species vary a lot in density, colour and finish, and timber changes with weathering and maintenance. Rather than asking which whole material category gets hotter, compare the actual surfaces you're looking at for your job.

Heat also raises questions about movement. Millboard states that because its boards use a resin-mineral composition and are 100% wood-free, they are stable compared with wood and wood-based composites, with acceptable movement of up to 0.2% currently stated. That doesn't mean you install them tight together. You still follow the manufacturer's requirements. For Enhanced Grain Millboard currently specifies 4mm between sides of boards, 1mm between board ends and 10mm between decking and a solid surface to aid drainage. Those are manufacturer installation requirements, not universal UK Building Regulations — another manufacturer may specify different gaps. We will cover that properly in What Gap Should You Leave Between Decking Boards?

Even with a relatively stable product, gaps still matter. Water needs somewhere to go, debris needs to be manageable and the deck needs appropriate separation from walls and fixed surfaces. Millboard specifically identifies clearance from solid surfaces as assisting drainage. A good installation isn't about getting the smallest possible visible gaps — it needs to look good and work correctly.

Fading, Reflective Glass And How To Design For Sun

Heat and UV are related but shouldn't be confused as the same issue. Outdoor materials are continually exposed to ultraviolet. Millboard notes that materials exposed to sunlight naturally weather and tone down over time. Some degree of natural weathering shouldn't automatically be read as failure, but it should be considered when you choose colour — think about how the whole space will mature, not just how the board looks new.

Reflective glass deserves particular attention because concentrated reflected sunlight is different from normal sunshine. Millboard advises avoiding reflective glass nearby where it could intensify heat build-up. We've seen this where large glazed elevations or a neighbour's glazing reflects sun onto a small area of deck and that patch gets much hotter than the rest. If you've got large south-facing glazing, it's worth checking where reflections fall at different times of day before finalising layout and colour.

In practical terms, if you're planning Millboard for a hot, sunny spot, think about colour first, then shade and layout. A lighter board in the main barefoot route, a slightly darker board for contrast where people wear shoes, a pergola or planting that gives you shade during peak afternoon sun — small design decisions like that make more difference than worrying about whether Millboard as a category gets hot.

Useful Guides

If you're weighing up temperature and colour, it helps to look at how the deck is actually used. Our guide on How to Maintain Composite Decking explains the simple cleaning routine that keeps surfaces pleasant underfoot, especially in sunny gardens where dust and pollen build up quickly.

Drainage and spacing play a bigger role than most people expect when a deck gets hot and stays damp afterwards, which is why Decking Drainage: How to Prevent Water Problems and What Gap Should You Leave Between Decking Boards? are worth reading alongside this one. For wider comparisons, Millboard vs Composite Decking: What's the Difference? and Is Composite Decking Slippery When Wet? cover how different boards perform underfoot in wet and dry conditions.

If you're still deciding on overall value and lifespan, How Long Does Composite Decking Last? and Is Millboard Decking Worth the Money? look at what determines real long-term performance beyond just board colour.