The performance of thermal protective clothing has become a growing concern to the textile industry during the past several decades. Developments are constantly being made in the protective fabrics market to improve protection against extreme heat while maintaining wearer comfort and mobility. Double needle bar knitted spacer fabrics have been produced from fire resistant yarns for use in thermal protective apparel. Past research of raschel knitted spacer fabrics has revealed desirable characteristics that may be eneficial for thermal protective clothign. No research has been conducted to determine how design changes can affect the thermal protective performance of spacer fabrics. Any research that will provide a better understanding of the design requirements of thermal spacer fabrics. Any research that will provide a better understanding of the designrequirements of thermal spacer fabrics will be beneficial to the textile indstry and may lead to the development of more effective fabrics for protection against extreme heat. The results of this research indicated that changes in fabric construction parameters can be used to optimize the thermal protective performance of raschel knitted spacer fabrics. Comparison of the spacer fabrics to commercially available baseline fabrics showed that the spacer fabrics performed competitively in thermal testing under certain conditions. Physical testing of the research fabrics showed that the spacer fabrics were stronger than the baseline fabrics. Based on these results, a thermal protective spacer fabric can be designed that insulates as well as or better than currently used fabrics but with the physical characteristics of a warp knitted fabric. 42 refs.