For an exterior facade, use 4mm ACP with 0.50mm aluminium skins; 3mm with 0.30mm skins is for signage and interiors, and 2mm is thin decorative only. The headline “4mm” tells you little on its own — the aluminium skin gauge is what stops the panel oil-canning and denting. A 4mm panel with 0.21mm skins is a signage panel dressed as facade. Always ask for two numbers: total thickness and skin gauge.
The three thicknesses and where each belongs
2mm: thin, light, decorative interior and small signage only. 3mm/0.30mm: signage, shopfronts, interior cladding, some low-rise soffits. 4mm/0.50mm: the standard for exterior building facades, because the thicker skins give flatness and rigidity over big spans. If a facade quote says 4mm without a skin number, treat it as unknown until confirmed.
Why skin gauge decides quality
The two aluminium skins carry the stiffness. Drop the skin from 0.50mm to 0.21mm and the same “4mm” panel oil-cans (visible waviness), dents on handling, and reads cheap on a facade. Reputable facade ACP uses 0.50mm skins; signage-grade uses 0.21–0.30mm. The core thickness makes up the rest of the millimetres but adds little stiffness.
Matching thickness to span and fixing
Bigger cassettes and wider panel spacing need the stiffness of 4mm/0.50mm. Tray and cassette systems especially rely on skin gauge to stay flat when folded at the edges. Tell the fabricator your panel sizes and fixing method, and let them confirm the thickness — do not let panel size outrun the gauge.
What to write on the enquiry
Specify: total thickness (4mm), aluminium skin gauge (0.50mm), core (FR/A2 for facades), coating (PVDF), RAL and gloss, and panel sizes. That one line filters out signage-grade material quoted at facade prices. A real factory answers all of it; a trader often dodges the skin gauge.
Frequently asked questions
What ACP thickness is used for facades? 4mm total with 0.50mm aluminium skins is the exterior facade standard; 3mm/0.30mm is signage and interior.
Why does aluminium skin gauge matter? The skins carry the stiffness. Thin 0.21mm skins oil-can and dent even at 4mm total; 0.50mm stays flat on a facade.
Is a cheap 4mm ACP the same as a real one? No — it usually has thinner skins (0.21mm) and often a PE core. Confirm skin gauge and core, not just the 4mm.
What thickness for signage? 3mm with 0.30mm skins, or 2mm for light interior decorative work.
Related: ACP buyer’s guide · ACP price 2026 · ACP colour selection.
Talk to the factory: GSM BuildTech (Beijing Guanshimao Technology Co., Ltd.) makes insulated aluminium panels, FR aluminium composite panels, standing-seam aluminium roofing and PVDF aluminium coil in Tianjin, China. Email sales@insulatedaluminumroof.com or WhatsApp +86 155 2274 6824 for factory-direct pricing. See the technical reference & FAQ.