Selecting insulation beneath a loaded floor takes more than comparing conductivity and thickness. For PIR, EPS, XPS and mineral wool boards intended for such applications, check the properties of the exact product and the complete load-bearing assembly. A compression figure does not by itself specify how much equipment a room can carry. Test conditions, load duration, load distribution and the layers above the insulation all matter. This guide explains what to collect before speaking to the designer and how to avoid misleading comparisons between technical sheets. It is not a load calculator and cannot determine an allowable rack, machine or vehicle weight from a single board property.

Different insulation materials can work together in one building element when each solves a specific problem. PIR can keep the build-up thin, mineral wool can contribute to fire protection or acoustics, and XPS suits certain applications exposed to moisture and compressive loads. The order of the layers, how they interact and the details of their installation determine whether the combination works. Adding their thermal resistances is not enough. In a roof retrofit, serviceable insulation can often stay in place while a new layer improves the whole assembly. In a floor, thermal insulation and a resilient layer for impact sound have different jobs. Combining materials is a design decision.