The thermal resistance of VIPs "per unit thickness" compares very favourably to conventional insulation. For instance, standard mineral wool has a thermal conductivity of 0.044 W/(m·K), and rigid polyurethane foam panels about 0.024 W/(m·K). This means that VIPs have about one-fifth the thermal conductivity of conventional insulation, and therefore about five times the thermal resistance (R-value) per unit thickness. Based on a typical "k"-value of 0.007 W/(m·K), the R-value of a typical VIP would be 3.5 m2·K/W (20 h·ft2·°F/BTU). To provide the same R-value, of rockwool or of rigid polyurethane foam panel would be required.