This paper reports on an experimental investigation on the effect of clothing thermal properties on the comfort sensations of wearers during sport activities. A sweating manikin"Walter" - was used to measure the clothing thermal properties (namely, thermal insulation, moisture vapor resistance and moisture accumulation within clothing) of five tracksuits. The average comfort sensations of five men wearing each of the five tracksuits were correlated with the thermal properties of the tracksuits measured from the sweating manikin - "Walter". It was found that the thermal comfort sensations during active sports were strongly related to the moisture vapor resistance and moisture accumulation within clothing. The overall comfort of sportswear during sports activities was very much related to the moisture related comfort sensations and clothing properties.