Anodised or powder-coated aluminium: how to choose the finish

When choosing an aluminium window, colour isn’t just aesthetics: it’s the coating that protects the metal for the decades that follow. And the two main routes — anodising and powder coating — aren’t simply “two ways to colour aluminium”: they’re two chemically different processes, with different appearances, colour ranges and long-term behaviour, especially near the sea.

This article sets out the differences honestly, to help you choose the right finish for your context. We won’t go into how the profile itself works or thermal breaks — for those, see the complete guide to aluminium windows and the dedicated article on thermal breaks. Here we focus purely on the surface: how it’s produced, what effect it gives, and how well it holds up.

Two different processes, not two “colours”

The underlying difference is simple but decisive.

Anodising is an electrochemical process: the profile is immersed in a tank and, using an electric current, the oxide layer that aluminium already forms naturally is grown in a controlled way. In effect, a protection the metal already has is thickened and made uniform. The colour isn’t a coating applied on top: it’s the metal itself, which after anodising can either stay natural or be dyed by letting a pigment penetrate the pores of the oxide, before sealing.

Powder coating, by contrast, is the application of a coating over the metal. The powder — usually polyester — is sprayed onto the electrostatically charged profile, then the piece is cured in an oven where it melts and polymerises to form a continuous, adherent film. Here the colour is a layer that sits on top of the aluminium, not within it.

Almost everything else follows from this basic difference: appearance, colour range, and behaviour in aggressive environments.

Aspect	Anodising	Powder coating
Nature	Grown metal oxide	Applied paint film (on top)
Where the colour sits	Inside the oxide layer	On top of the metal
Typical effect	Metallic, natural, satin	Wide RAL range, matt/gloss/wood-effect
Colour range	Limited (metal tones, bronzes, blacks)	Practically unlimited
Reference quality mark	—	QUALICOAT (voluntary)

The figures and numerical ranges you’ll find further on are indicative, given as examples: they give an order of magnitude, not a guaranteed technical specification. The technical data sheet for the chosen system and treatment remains the only certain reference.

Appearance: metallic look versus a full colour range

This is the difference you notice at a glance, and often the one that guides the choice.

Anodised aluminium has a metallic, natural appearance. It’s visibly aluminium: the finish is typically satin, with a depth that lets you glimpse the metal beneath. The range is inherently narrower by nature — silver/natural tones, shades of bronze (from champagne to dark walnut), black, a stainless-steel-like effect. These are “technical” colours, well suited to contemporary architecture and to façades where a restrained, material-led look is wanted. What anodised aluminium generally doesn’t do is bright red, vivid green, or opaque white: these aren’t tones that come out well when dyeing the oxide.

Powder coating, on the other hand, opens up the full colour range: in principle, any RAL shade, with a choice of surface textures:

• matt (very much in demand today, a contemporary, low-reflectivity effect),
• gloss (more classic, more reflective),
• textured / micaceous (a slightly rough surface, with a micro-texture that hides fingerprints and scratches better),
• wood-effect (sublimation: a film with a wood grain transferred onto the coated profile, giving the look of timber with the durability of aluminium).

Aesthetic requirement	Best-suited finish (by way of example)
Metallic/natural look, modern architecture	Satin anodised
White, bright colours, precise RAL shades	Powder-coated
Wood-grain effect	Powder-coated + wood-effect sublimation
A surface that hides fingerprints	Powder-coated, textured/micaceous
Understated bronze/champagne	Anodised (or powder-coated in a matching shade)

An honest note: on powder-coated finishes, the wood-effect gives a very good aesthetic result, but to the touch it remains different from real wood. Anyone after the genuine warmth of timber should also weigh up a material comparison; here we’re staying with aluminium.

Durability and how it ages

Both treatments, done properly, last many years. The difference lies in how they age.

Anodised aluminium, being an oxide of the metal itself, doesn’t “peel”: there’s no film that can flake off. The main risk, on anodised layers of insufficient thickness or poorly sealed, is a slow lightening or a loss of tonal uniformity over the long term, more noticeable on very sun-exposed surfaces. With adequate thickness, the colour stays stable for a long time. The thickness of the anodic layer is measured in microns and is one of the parameters that affects durability: as an indication, higher thicknesses are called for on exposed exteriors than for interior use. The exact figures depend on the class chosen and should be read from the treatment’s data sheet — anything quoted from memory is only an order of magnitude.

Good-quality powder coating holds colour well and resists UV rays, especially in polyester formulations designed for outdoor use. The market reference for powder coating quality is the QUALICOAT mark: a voluntary quality mark that certifies the treatment was carried out to certain process requirements. We won’t go into its numerical specifications; suffice it to say that a coating compliant with a recognised standard is a good sign, whereas a “generic” undocumented coating is a closed box. The theoretical limit of powder coating, being a film over the metal, is that a deep impact reaching the metal creates a point where corrosion can start; with anodised aluminium this issue is structurally less present, because the colour is the treated metal itself.

Behaviour over time	Anodised	Powder-coated
Possible degradation type	Slow lightening/tonal unevenness	Very good colour retention; risk at points of deep impact
Can it flake?	No (it’s an oxide of the metal)	In theory, yes, if poorly applied or struck deeply
Quality reference	Micron thickness + sealing	QUALICOAT (voluntary)
UV resistance	Good with adequate thickness	Good in outdoor-grade polyester formulations

The indications above are qualitative and indicative: real-world behaviour depends on exposure, maintenance, process quality and environment.

Aggressive environments: the case of salt exposure

The toughest test for a finish on aluminium is the coast. Airborne salt is aggressive towards metals, and a house a few hundred metres from the sea puts far more stress on windows than one further inland.

In a marine environment, the continuity and integrity of the coating become crucial. Here, powder coating compliant with a recognised standard tends to be the better-suited option, because it provides a continuous barrier between metal and environment; for particularly exposed locations there are also treatment classes designed for marine/industrial atmospheres, to be agreed at order stage. Good-quality anodised aluminium also performs well, but requires adequate thickness and sealing to withstand salt exposure.

The practical point is different: state the context when requesting a quote. “House 300 metres from the sea, exposed to salt-laden winds” is information that changes which treatment class should be specified. A standard finish, designed for an inland context and fitted at the seafront, can degrade sooner than expected — not because it’s poor quality, but because it’s the wrong treatment for that environment.

Dual-colour: different inside and outside

One advantage of aluminium is how easily it allows dual-colour finishes: one colour outside and a different one inside the same window. This is managed very cleanly, because a thermal-break profile is already physically split into two parts (external and internal) joined by the insulating bar.

Typical cases:

• dark outside, white inside: a modern façade with anthracite or bronze outside, a bright, neutral interior;
• exterior matching the façade, wood-effect interior: for those seeking harmony with the interior furnishings;
• bronze anodised exterior, light powder-coated interior: a combination of both worlds.

Dual-colour is more straightforward on powder-coated finishes (two separate passes on different sides), but it’s achievable in various combinations. It needs to be defined at order stage, as it affects fabrication and sometimes lead times. If the priority is the aesthetics of a large glazed opening, it’s worth considering alongside the type of opening: see for example sliding and lift-and-slide doors, where the amount of frame on show makes the colour choice even more visible.

Maintainability: purely as a comparison

Without turning this into a maintenance guide (that isn’t the purpose of this article), it’s worth framing the difference as a comparison.

Broadly speaking, both finishes require little upkeep: well-treated aluminium is never repainted and doesn’t need the care that timber does. The qualitative difference is that, in the event of surface damage, a powder-coated finish can show a localised spot where the film has been compromised, whereas anodised aluminium — since the colour is part of the metal — is more “all of a piece”. In heavily exposed environments (sea, industrial dust), periodic cleaning preserves the look, whatever the finish. These are points of comparison, not instructions: always refer to the coating manufacturer’s guidance for correct practice.

How to decide

To sum up, the choice between anodised and powder-coated comes down to a few concrete factors:

1. Desired aesthetic: for a metallic/natural look, anodised; for a precise, vivid or white colour, or the wood-effect, powder coating is almost mandatory.
2. Environment: near the sea or in aggressive atmospheres, the treatment class matters more than anything else — to be stated at order stage.
3. Colour range: powder coating for maximum RAL freedom; anodised for the metal/bronze palette.
4. Dual-colour: achievable with either, more straightforward on powder-coated finishes.

There’s no finish that’s “best” in absolute terms: there’s the one that’s right for your context, your aesthetic and your exposure. It’s worth starting from the real context and being offered the finish that suits it, with the quality reference made explicit.

To get the full picture on aluminium — profiles, performance, prices — see the dedicated aluminium windows page and, if you’re still comparing materials, the in-depth PVC versus aluminium comparison.

When it’s NOT worth it

There are cases where pushing for a particular finish brings no real benefit, and it’s right to say so.

• When you’re chasing a vivid colour through anodising: if you have a red, a blue or an opaque white in mind, anodising isn’t the right route. Forcing it gives mediocre results compared with a powder-coated RAL shade.
• When you choose the wood-effect expecting real timber: the wood-effect on aluminium is visually convincing, but it remains a surface finish. If you want the material timber for its warmth and touch, that’s a different evaluation.
• When you ignore a marine context: insisting on a standard finish “because it’s cheaper” at the seafront is a false saving. There, the treatment class matters more than the finish’s list price.
• When dual-colour is just a whim on a tight budget: it’s attractive and functional, but if budget is the main constraint, a uniform, quality finish is preferable to a dual-colour finish on a mediocre treatment.
• When you chase the “highest possible” micron thickness without reason: thicknesses and classes should be sized to the real exposure. Paying for an oversized class in a protected interior context is spending with no return.

In all these cases the rule is the same: start from the real use, not from the finish’s label.

FAQ

Is anodised aluminium more durable than powder-coated? Not in absolute terms: they’re durable in different ways. Anodised aluminium doesn’t flake because it’s an oxide of the metal itself; good-quality powder coating holds colour very well and acts as a continuous barrier. What matters most is the quality of the process (thickness/sealing for anodising; compliance with a standard such as QUALICOAT for powder coating) rather than the type itself. Comparisons should be taken as orders of magnitude.

Can I have any RAL colour with aluminium? With powder coating, in principle yes: the entire RAL range, with a matt, gloss or textured finish. With anodising, no: the range is narrower and tied to metal, bronze and black tones.

Does dual-colour cost a lot more? Dual-colour (a different colour outside and inside) is achievable with aluminium in a fairly clean way, thanks to the thermal break that splits the profile into two parts. It affects fabrication and sometimes lead times; it needs to be defined at order stage. For an accurate estimate, it’s best to request a dedicated quote.

I live near the sea: what should I choose? What matters most isn’t so much “anodised versus powder-coated”, but the treatment class appropriate to the marine environment, stated at order stage. There are coating classes designed for salt-laden/industrial atmospheres; good-quality anodised aluminium also performs well. The deciding factor is stating your distance from the sea and level of exposure.

What does it mean that a coating is QUALICOAT? QUALICOAT is a voluntary quality mark for powder-coated aluminium: it indicates the treatment was carried out to certain requirements. It’s a good sign of process reliability. It doesn’t make the finish “indestructible”, but a coating compliant with a recognised standard offers more assurance than a generic, undocumented one.

Is the wood-effect the same as real timber? It’s a very good aesthetic result, achieved by transferring a wood grain onto the coated profile, with the durability and low maintenance of aluminium. Visually it’s convincing, but to the touch it remains aluminium: anyone after timber for its genuine warmth should evaluate it separately.

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If you already have a sense of your home’s context — exposure, distance from the sea, style — and want to work out which finish makes sense for your windows, start from a concrete assessment. You can request a quote describing your context: that’s how the right finish is identified, not from an abstract colour chart.