Biobased composites are increasingly used. One of the most frequently used material is hemp shives, which is agricultural waste. However, as the quantities of this material are lacking, there is a tendency towards finding new and more available materials. Corncob and sawdust are bio by-products that have great potential as insulation materials. In order to use these aggregates, it is necessary to examine their characteristics. New composite materials based on sawdust, corncobs, polystyrene granules and the mixture of lime and plaster as the binder, were tested within this research. This paper presents the properties of these composites obtained by determining the porosity of samples, volume mass, water absorption, airflow resistance and heat flux, which was followed by calculation of the thermal conductivity coefficient. Three mixtures of the new composite material, whose samples were 1cm-5cm thick for each type of mixture, were investigated. The aim of this research was to analyze the results of different mixtures and sample thickness in order to determine the optimum composite material of the proper thickness so that the best possible thermal and sound insulation could be obtained. New composite materials can be used as an alternative to conventional materials.