The article suggests the technique of determining true density of the foamed polymeric and composite materials by means of the hydrostatic weighing; partial filling of open pores along the perimeter of sample is taken into account. Due to the fact that direct methods of measurement of materials porosity are extremely difficult, in ceramics technologies this indicator is often estimated by determination of other properties which are directly depending on the porosity. Such indicators determine material density (true, seeming, relative) and water absorption. The true density is a physical constant for individual substance and depends on its structure. As for ceramics, its size depends on density of atoms packing in crystals and the chemical composition of a vitreous phase. The seeming density is the relation of body weight to total volume occupied by it, including pores. The Relative density is determined as the relation of the seeming density to true density (expressed in shares of unit or as percentage). It represents a volume fraction of strong substance in material. The water absorption is the relation of water mass absorbed by a ceramic body at full saturation, to the mass of a dry sample. This indicator is often used in the production conditions for characterizing the agglomeration extent, quality of products and compliance with standard requirements. Having measured the above characteristics, it is possible to point out the general, open and closed porosity. The true or general porosity is the total volume of all pores opened and closed, expressed as percentage to the total amount of material. This size is designated by Pi and numerically is equal to the sum of the closed and open porosity. The seeming or open porosity is the relation of volume of all open pores of a body (filled by boiling water) to total volume of material, including the volume of all pores. The size is designated via the personal computer and expressed in %.

В работе предложена методика определения истинной плотности вспененных полимерных и композиционных материалов гидростатическим взвешиванием. При измерении учитывается частичное заполнение открытых пор по периметру образца.