In the recent decades, due to decrease in energy resources and a sharp rise in the cost, optimization of energy consumption has been considered by many countries. Many researches and studies have been conducted in the field of optimization of the textiles thermal insulation properties. Textile materials are combination of air and fibers. Thermal conductivity of air is much lower than the fibers. The air between the fibers and textiles plays an important role in thermal insulation. These days, nano technology has affected many aspects of human life. The function of materials in the nano scale is due to high specific surface area. Use of ceramic nanoparticles with suitable binders can improve thermal properties, while the mechanical properties of textiles are maintained. Ceramic nanoparticles have a high melting point and low thermal conductivity and can improve the thermal properties of textiles. The main purpose of this work is to increase the fabric thermal insulation properties using silica nanoparticles. Silica nanoparticles were coated onto the fabric in two different forms of powder and emulsion. To create uniform coating, polyester/viscose fabric has been treated with silica nanoparticles through two types of coating method i.e. knife coating and dip coating. Polyethylene glycol, polyurethane and acrylate were applied as binders. After preparing the samples, thermal properties, abrasion stability, washing-cleaning stability and flexural stiffness of the samples have been measured and compared. software and Duncan tests have been used for statistical analysis of the results. Results showed that, the temperature difference between the hot side (in contact with the hot plate) and the cold side of the samples increases, with increase in the percentage of silica nano particles. In other words, the thermal conductivity of samples reduces with increase in the percentage of silica nano particles. The coated samples with knife coating method showed more uniform distribution of silica nanoparticles on the surface of the fabric. This coating method covers the entire surface of the fabric uniformly with nanoparticles and consequently leads to a significant decrease in the thermal conductivity of the fabric. Polyurethane binder in comparison to acrylate binder revealed better thermal properties, comfort properties and bending rigidity. Sample coated with eight percent of silica nanoparticles, using knife coating method, showed the best thermal insulation properties. Pad process was used to improve the fabric flexural stiffness properties. Key words: Thermal conductivity, silica nanoparticles, thermal insulation, hot-plate, flexural stiffness, knife coating, dip coating