Why a large cold storage is equipped with concrete floor sandwiched with XPS panels, instead of normal PU floor ?

For large cold storage floors, the composite structure of concrete with XPS (extruded polystyrene board) insulation embedded is widely adopted instead of conventional PU insulation boards. This is mainly a comprehensive consideration of load bearing, impact resistance, moisture proofing, freeze-thaw stability, construction and long-term reliability, especially for medium and large cold storages with frequent forklift operation and heavy stacked goods.

Conventional PU boards have relatively low compressive strength. Under long-term rolling by internal combustion and electric forklifts and concentrated pallet loads, the core PU foam is prone to compression collapse, cracking and depression. Once the insulation layer is damaged, cold loss occurs rapidly, resulting in floor hollowing, frost heave and frost formation.

XPS features a dense closed-cell structure with much higher compressive strength. When combined with cast-in-situ reinforced concrete, the concrete bears the mechanical load while the XPS provides thermal insulation, which is not easy to crush under heavy loads.

Besides, the floor is where heat and moisture converge. Water vapor from the subsoil easily causes frost heave under low temperature. PU foam has higher water absorption. If the waterproof layer fails, water entering the PU foam freezes and expands, destroying the insulation permanently and cannot be dried easily. XPS has continuous closed cells, low water absorption and excellent vapor resistance. It also shows good dimensional stability under sustained low temperature with little shrinkage, reducing delamination gaps. Assembled PU boards have numerous joints that form cold bridges.

In terms of cost, maintenance and fire safety, XPS also has advantages for large-area flooring. Although PU has a better thermal conductivity, it is more suitable for walls and ceilings without heavy mechanical loads. The XPS-and-concrete floor trades minor thermal performance for decades of stable service and fewer repairs.

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