Sportswear base layer provides an important function for physiological comfort. This book presents the investigation of base layer winter active sportswear fabrics with good comfort properties, made of natural and synthetic fibres and their blends. Polyester, wool and bamboo fibres were selected for this study. Polyester is the most common fibre used in sportswear, wool is increasingly being used in sportswear and bamboo is a relatively new fibre that offers properties suitable for base layer sportswear. Bamboo is also regarded as a green and eco-friendly fibre. Preliminary experiments were carried out to find the liquid moisture transfer performance of knitted fabrics made from each selected single fibre. Experimental single jersey sample fabrics were produced from different fibre blends of polyester, wool and bamboo. The comfort properties selected for evaluation and analysis were liquid moisture transfer, thermal conductivity, warm/cool feeling, stiffness and number of contactpoints between fabrics and the skin. This book will be useful to academics and professionals in the Textile Technology field especially those related to sportswear and performance apparel applications.