The 75mm Isotherm is underspecification as a stand-alone R-value. In fact, the 75mm Isotherm Insulation is ideal as a top up in homes installed with the 100mm Isotherm. Our 75mm Isotherm Price is very affordable.
Should this product be installed in the roof space there will most certainly be a difference however ideally you would want to install the 145mm Isotherm to be SANS compliant? For more info on the Isotherm, Insulation products read this page.