Guides / Facade Systems

ACP sheet price, 3 mm vs 4 mm: what the thickness actually buys

Q: How much does an ACP sheet weigh per square metre?

Between roughly 3.5 and 5.5 kg per square metre for polyethylene-core panels, and around 7.5 kg for a mineral-core A2 build. The figure follows the skins and the core: front plus rear skin in metres multiplied by 2,700, plus core in metres multiplied by 920, gives kilograms per square metre for a PE core.

Most buyers compare a 3 mm and a 4 mm aluminium composite panel as if the extra millimetre were the product. It is not. The number that moves the price, the weight and the wind performance is the aluminium skin gauge, and the same nominal thickness can be built with skins that differ by a factor of two. This page sets out the build-up, the arithmetic that turns a skin thickness into kilograms per square metre, where 3 mm stops being adequate, and the six specifications to ask for before a rate means anything.

Quick answer

A 3 mm and a 4 mm ACP sheet differ in core thickness, not necessarily in aluminium content. The price follows the skin gauge, the alloy, the core type and the coating, so a 4 mm panel with 0.21 mm skins can cost less than a 3 mm panel with 0.50 mm skins. Thickness matters for stiffness and for the fold geometry at a return; skin gauge matters for wind load, flatness, corrosion reserve and the metal value of the sheet.

The quick way to read a quotation is to ask for four numbers rather than one: front skin, rear skin, core type, coating system. A quote that gives only “4 mm” has told you the least important of the five.

What is inside a 3 mm and a 4 mm panel

An ACP is a sandwich: two aluminium skins bonded to a thermoplastic or mineral core. The nominal thickness is the total, so a 3 mm panel with 0.30 mm skins carries a 2.40 mm core, and a 4 mm panel with the same skins carries a 3.40 mm core. The aluminium is between 14 and 33 per cent of the section, depending on how the skins are specified.

The Chinese product standard GB/T 17748 defines the panel by its total thickness and by the skin thickness, and it is the skin thickness that appears in the tolerance table. That is the reason two suppliers can both quote “4 mm, 0.30 skin” and ship panels that weigh different amounts: the tolerance on the skin is not the tolerance on the total.

Build-up	Front / rear skin	Core	Mass, kg/m²
3 mm, light	0.21 / 0.21 mm	2.58 mm PE	about 3.5
3 mm, standard	0.30 / 0.30 mm	2.40 mm PE	about 3.8
4 mm, standard	0.30 / 0.30 mm	3.40 mm PE	about 4.8
4 mm, heavy skin	0.50 / 0.50 mm	3.00 mm PE or FR	about 5.5
4 mm, mineral core	0.50 / 0.50 mm	3.00 mm A2 core	about 7.5

Mass is arithmetic from the densities: aluminium at 2,700 kg/m³ (EN 1999-1-1) and a polyethylene core at roughly 920 kg/m³. A mineral-filled core is heavier, which is why the A2 build sits at the bottom of the table.

The arithmetic, so you can check any quote

Mass per square metre is the sum of the two skins and the core, each one thickness in metres multiplied by density:

kg/m² = (t_front + t_rear) × 2,700 + t_core × 920

For a 3 mm panel with 0.30 mm skins the front and rear together are 0.60 mm, which is 0.0006 m × 2,700 = 1.62 kg/m². The 2.40 mm core adds 0.0024 × 920 = 2.21 kg/m². Total 3.83 kg/m². Run the same figures on a 4 mm panel with 0.21 mm skins and the answer is 1.13 + 3.13 = 4.26 kg/m² — heavier than the 3 mm panel, and carrying less aluminium.

That comparison is the whole argument. Weight is not the same thing as metal content, and it is the metal content that a buyer is paying for when the aluminium price moves.

Where 3 mm stops being enough

Three millimetres is a perfectly serviceable panel, and most interior and low-rise cladding uses it. It stops being the right choice in four situations, and each one is a calculation rather than a preference.

Wind load on a tall facade. Stiffness rises with the cube of the section depth, so the panel span between rails and the suction pressure on the elevation decide whether a 3 mm sheet deflects visibly. A 4 mm panel at the same rail spacing deflects less, which usually buys a wider rail spacing and fewer fixings rather than a stronger wall.
Returns and folds. Riveting a return needs core depth to route. A 3 mm panel with 0.30 mm skins leaves a 2.4 mm core to rout, and the fold radius has to fit inside it; the same detail on a 4 mm panel is easier to execute and holds its edge straighter.
Flatness on large modules. Panels wider than about 1.2 m in a dark colour show every deviation. The extra core depth of a 4 mm panel resists the oil-canning that makes a large sheet look wavy in raking light.
Fire performance. The reaction-to-fire class comes from the core, not the thickness, and it is classified under EN 13501-1. An unfilled polyethylene core typically reaches a low class; a flame-retardant core typically reaches B-s1,d0; a mineral-filled core is what reaches A2-s1,d0. If the specification calls for A2, the panel is a different product at any thickness, and it is priced as one.

What actually moves the rate

Variable	Effect on price	How to verify it
Skin gauge	Largest single factor; metal value scales with it	Ask for front and rear gauge in mm, with tolerance
Alloy and temper	3003 and 5005 behave differently in a fold; both are common	Mill certificate naming alloy and temper
Core type	PE, FR and mineral cores are three products at three prices	EN 13501-1 classification report, not a catalogue logo
Coating	Polyester, PVDF and anodised differ in film thickness and warranty	Coating thickness in µm and the resin system named
Aluminium price	The metal component is indexed, which is why quotes carry a validity date	Quote validity period, and what happens at expiry
Quantity and packing	Set-up, cutting and crate costs divide across the order	Packing list and the units per crate

Because the metal is the volatile part, the LME aluminium price is the benchmark used for indexation in aluminium contracts, and it is the reason a rate held for six months is a rate someone is carrying risk on. A supplier who will not put a validity period on a per-square-metre figure has not priced the metal properly.

Six things to put in the enquiry

Front and rear skin gauge. In millimetres, with the tolerance. Not “0.3” as a marketing figure.
Alloy and temper. 3003 H14 and 5005 H34 are the usual answers; the fold behaviour and the corrosion reserve differ.
Core type and fire class. PE, FR or mineral, with the EN 13501-1 class written out in full, including the smoke and droplet suffixes.
Coating system and film thickness. Polyester at 25 µm and PVDF at 25 µm are not the same warranty, and neither is anodising.
Panel size and the rail spacing it will span. The span is what turns a thickness into a structural choice.
Quantity, packing and the delivery basis. A per-square-metre figure without these is a figure for a different order.

Send the elevation with the rail layout if you have it. A supplier who can see the spans will tell you which of the two thicknesses the facade actually needs, and that answer is worth more than a discount on a panel that deflects.

Frequently asked questions

Is 4 mm ACP better than 3 mm?

Better for stiffness, for fold geometry and for flatness on large modules. Not automatically better for the facade, because a 3 mm panel with heavier skins carries more aluminium than a 4 mm panel with light skins, and it costs more for that reason. The right question is which skin gauge the wind load and the detail require, at a span you have stated.

Why is a 4 mm panel sometimes cheaper than a 3 mm panel?

Because the nominal thickness is not the metal. A 4 mm sheet built with 0.21 mm skins contains about 1.13 kg of aluminium per square metre, while a 3 mm sheet with 0.50 mm skins contains 2.70 kg. The second is the more expensive product even though the number is smaller. Compare skin gauges before comparing totals.

How much does an ACP sheet weigh per square metre?

Between roughly 3.5 and 5.5 kg/m² for polyethylene-core panels, and around 7.5 kg/m² for a mineral-core A2 build. The figure follows the skins and the core: (front + rear skin in metres) × 2,700 plus (core in metres) × 920 gives kilograms per square metre for a PE core.

Does thickness decide the fire rating?

No. The core decides it. Reaction to fire is classified under EN 13501-1, and the class is a property of the core chemistry: unfilled polyethylene typically lands in a low class, a flame-retardant core typically reaches B-s1,d0, and a mineral-filled core is what reaches A2-s1,d0. Thickness affects how long a panel holds together, not which class it is in.

What is the usual skin thickness for exterior cladding?

Exterior work normally starts at 0.30 mm skins and rises to 0.40 and 0.50 mm as the span, the height or the wind pressure increases. Interior and signage work commonly uses 0.21 mm. Ask what the sheet will span, and the gauge follows from that rather than from a habit.

How long is a quoted ACP rate valid?

It should be stated with the quote, because the aluminium component is priced against an index. A validity period of days or a few weeks is normal; a figure offered with no expiry is either already loaded for the risk or about to be revised when the order is placed.

Sources

GB/T 17748, Aluminium-plastic composite panels, for the definition of the product by total thickness and skin thickness, and for the tolerance tables that follow the skins rather than the total.
EN 1999-1-1, Eurocode 9: Design of aluminium structures — General rules, for the density of aluminium, 2,700 kg/m³, used in every mass figure on this page.
EN 13501-1, Fire classification of construction products and building elements — Part 1, for the reaction-to-fire classes and the s1 and d0 suffixes quoted above.
EN 485-2, Aluminium and aluminium alloys — Sheet, strip and plate — Part 2: Mechanical properties, for the alloy and temper designations used in the enquiry list.
London Metal Exchange, LME Aluminium, for the official price used as the benchmark for indexation in aluminium contracts.
The 3 mm and 4 mm build-ups, the 0.21 to 0.50 mm skin band and the panel sizes are the specification on our aluminium composite panel page.

The mass figures are arithmetic from the densities and thicknesses printed beside them and can be recomputed from the formula shown. No unit price is published here: an ACP rate is a metal index plus a build-up, and a figure without the skin gauge, the core class and the quantity behind it would be out of date before it was read.