Metal composite panel (ACP)

What is a metal composite panel?

A metal composite panel is a flat cladding sheet that has two thin aluminium skins bonded to a core. It is often called an aluminium composite panel (ACP) or aluminium composite material (ACM). The panel is cut, folded and fixed to a substructure, and it is a common outer layer for modern flat facades. The manufacturer 3A Composites, for example, describes its panels as two 0.5 mm aluminium cover sheets with a core between them. Its panels come in 3 mm and 4 mm thicknesses. UK guidance calls the same product metal composite material (MCM).

How is an ACP built, and why does the core matter?

The core sits between the two skins. It can be a polyethylene (PE) plastic, a polymer with a flame-retardant mineral filler, or a mineral-filled core that the maker classes as non-combustible. The core is hidden once the panel is fixed, so the choice is easy to miss at the design stage. 3A Composites states that its Alucobond Plus panel has a mineral-filled polymer core. The maker says it achieves better fire ratings than panels with a black PE core. That is a manufacturer statement about its own products, so the fire rating of any other panel needs its own test report.

What do the fire classes of an ACP mean?

Reaction to fire in the EU is classified under EN 13501-1. Commission Delegated Regulation (EU) 2016/364 sets the classes A1 to F, where A1 has the highest performance and F the lowest. Classes A2, B, C and D carry two extra marks. The smoke mark runs from s1 (least smoke) to s3, and the droplet mark runs from d0 (no flaming droplets in the test) to d2. The table shows how the two mineral-core products of one manufacturer are classified.

Product (3A Composites)	Core, as described by the maker	EN 13501-1 class
Alucobond Plus	Mineral-filled polymer, fire retardant, 70% mineral content	B-s1, d0
Alucobond A2	Mineral-filled core with polymer binder, non-combustible, more than 90% mineral content	A2-s1, d0

A class applies to the tested panel with its stated thickness and test set-up. It does not describe every panel with the same core name, so ask for the classification report of the exact product.

Why are PE-core panels restricted on high-rise facades?

A PE core is a plastic, and a plastic core is a combustible material inside the wall. The restrictions follow from the wish to keep combustible material off the outside of tall buildings. After the Grenfell Tower fire, the UK government stated that new buildings over 18 metres could not have combustible materials on their external walls. It also moved to speed up the replacement of unsafe ACM cladding of the type used on Grenfell Tower.

Date	UK measure	Scope
29 November 2018	Regulations laid in Parliament to ban combustible materials on external walls	New buildings over 18 metres, including those containing flats
1 June 2022	Approved Document B update bans metal composite material panels with unmodified polyethylene core	All new buildings at any height

The 2022 update also applied the 2018 ban on combustible materials in external walls to hotels, hostels and boarding houses. These are UK rules. They do not set the position in Slovakia.

What does Slovak fire law say about cladding on external walls?

The fire safety decree of the Ministry of the Interior, vyhláška 94/2004 Z. z., covers the construction and use of buildings. In the version valid from 1 January 2019, § 48 covers surface finishes and claddings of external walls. They must not contribute to the spread of fire. The same paragraph says this is also treated as met when the procedure of a special regulation is followed. Section 11 of the decree adds that flame spread over the products on an external wall surface is stated as a flame spread index. A type test gives that index. This page does not list the class a particular building needs, and it does not claim that Slovakia bans any panel type. The designer sets the fire classification of the wall build-up for each project and, where needed, agrees it with the fire authority.

How is a metal composite panel different from a rainscreen cladding?

An ACP is a type of panel. A rainscreen is a system: an outer layer with a ventilated gap behind it, fixed to a substructure. ACP is often used as the outer layer of a rainscreen cladding or of a ventilated facade. The choice of panel and the choice of system are separate decisions. A panel from a different material family, such as fibre-cement cladding, has its own fixing rules and fire data.

What should you check before specifying an ACP panel?

Start with the core. Ask the supplier in writing which core the panel has, and ask for the classification report under EN 13501-1. 3A Composites recommends combining its Alucobond Plus or A2 panels with non-combustible mineral insulation for a fire-resistant, rear-ventilated facade. The panel is only one layer of that wall, so the insulation and fixings belong in the same fire review. The fixing details sit in the facade substructure.

It also helps to read the specification as a whole. A clause that says only "aluminium composite panel, fire-rated" leaves the core open. A supplier can then substitute a different product without the designer noticing. Name the core type in the specification. Name the classification the report must show. Require that the installed product is the one that was tested. A short written check at delivery, comparing the panel label with the data sheet, catches most substitutions before the panels reach the wall.