This study aimed to validate the summation methods suggested by ISO 9920. Twenty seven items from an ambulance personnel clothing system were selected for testing. The basic insulation of each garment item (Iclu) was calculated based on the thermal manikin tests. More than 100 realistic clothing combinations were compiled and basic insulation (Icl) of these ensembles was calculated according to ISO 9920. These were ranked after the calculated insulation, and 14 sets covering insulation from 0.63 to 3.33 clo were measured on the thermal manikin for acquiring the basic clothing insulation (Icl). Regression analysis was used to compare the summed and measured Icl values. The difference between values varied from -18 to 12%. The highest percentual difference was for the lightest clothing sets, while the absolute differences were similar over the whole insulation range ranging between -0.17 to 0.18 clo with an average difference of 0.02 clo (-0.16%). All basic insulation values stayed very close to the line of identity (R2=0.98). The summation equation gave, in the case of this ambulance clothing system, very close results to the measured values. This encourages evaluating and selecting protective clothing combinations for thermal comfort based on individual item measurements.
Keywords: Basic insulation; Garment item; Modelling; Optimal clothing selection; Protective clothing; Standard method; Thermal comfort.