Sandwich panels - two metal skins bonded to an insulating core - are the most common cladding for modern steel buildings because they combine structure, insulation, and finish in one product. They are fast to install, energy-efficient, and available in many configurations. Choosing the right panel is about matching the core, the thickness, and the facings to the building's climate and use.What a Sandwich Panel Is
A sandwich panel is a composite of two profiled steel facings (typically 0.4–0.6 mm) with a rigid insulating core between them, bonded under pressure. The panel carries wind loads as a structural element spanning between purlins and girts, while the core provides thermal insulation. Panels are made to national product standards - in China, GB/T 23932 (2025 edition) applies.
Core Types - The Key Decision
|
Core |
Insulation |
Fire Behavior |
Moisture Resistance |
Typical Use |
|
EPS (expanded polystyrene) |
Good |
Flammable - limited in fire-rated buildings |
Poor - absorbs water if damaged |
Economy roofs and walls |
|
XPS (extruded polystyrene) |
Good |
Similar to EPS |
Better than EPS |
Cool rooms, humid areas |
|
PIR / PUR (polyurethane) |
Excellent |
Better fire performance, low smoke |
Good |
High-performance, fire-rated buildings |
|
Rock wool (mineral fiber) |
Good |
Non-combustible, fire-rated |
Good |
Fire walls, workshops, code-driven projects |
Choosing Thickness and Facings
Panel thickness (typically 50, 75, 100, or 150 mm) is selected to meet the local thermal requirement - the higher the insulation demand, the thicker the core. Facings are chosen for durability and appearance: galvanized, pre-painted steel (PPGI), or special finishes such as PVDF for coastal or premium projects. For roofs, the top facing profile and its drainage ability matter; for walls, flat or micro-rib profiles give a cleaner look.
Installation and Detailing
Sandwich panels fail at details, not at the panel itself:
Panels must span between supports at or below the manufacturer's maximum spacing.
Joints, laps, ridges, eaves, and flashings follow the supplier's installation details; sealants and fasteners must match the specification.
Panels are cut on site only where unavoidable; the cut edges are sealed and protected.
Long panels require careful handling to avoid damage - panels are more delicate than they look.
Buyer's Checklist
Ask for the panel specification: core type, thickness, facing gauge and coating, and the fire class.
Confirm the insulation performance (U-value) meets your local requirement.
Request the manufacturer's installation details and flashing package with the order.
For fire-rated buildings, confirm the core is rock wool or PIR with the required rating - EPS is not acceptable where fire codes are strict.
A sandwich panel building is only as good as its specification and its detailing. A cheap panel with poor detailing will leak, sweat, and sag; a correctly specified system stays tight, warm, and maintenance-free for decades.