The thermal property of fabric is very important for both its thermal comfort and protection against challenging weather conditions. Although some research has reportedly been done on the dimensional and some of the mechanical properties of rib knit fabrics, no detailed study about the thermal properties of rib knit fabric could be seen. In this study, the natural and forced convective heat transfer characteristics of rib knit fabric have been analysed. The effect of rib design and other fabric properties such as fabric density and air permeability on thermal behaviour have been considered It has been noted that a decrease in rib number of the order of 3x3, 2x2 or 1x1 leads to a decrease in heat loss due to an increase in the amount of air entrapped between the face and the back loop. The results also indicated that as the fabric gets tighter so the heat loss lessens, due to reduced air permeability, i.e., reduced air circulation within the fabric. Thus, it results that when the fabric design (1x1 rib, 2x2 rib, 3x3 rib, etc) is taken into consideration, the conductive heat loss due to fibres and air gaps becomes more important than the heat loss due to air circulation (convective heat loss). However when the fabric density for each fabric design is taken into consideration, the heat loss due to air circulation (convective heat loss) becomes more important than the conductive heat loss due to fibres and air gaps.