The paper studies the relaxation characteristics of butadiene-nitrile rubber (BNR) and thiokol-based compositions, determines their main elastic-strength properties, which is important for assessing their operation under real conditions. The dependence of the properties of elastomeric compositions based on BNR on the thiokol content is considered. It is revealed that the introduction of thiokol into BNR-based compositions leads to a significant decrease in viscosity compared to a similar composition containing dibutyl phthalate. It is shown that the glass transition temperature decreases insignificantly, by a maximum of 3 °C at a thiokol content of 20 parts by weight, and in this case, in the BNR-based composition, thiokol acts as a softener. It is revealed that the introduction of thiokol from 20 parts by weight into BNR-based compositions leads to a significant increase in the elasticity of the material, and a further increase in the thiokol content in the system leads to a decrease in elasticity, which is associated with a decrease in the degree of crosslinking of the material. It was determined that the introduction of thiokol into the system leads to a slight increase in the modulus at 100% elongation, while the strength characteristics are reduced by no more than 1.5 times, the elastic properties of the compositions also increase and the Shore A hardness decreases. It was found that the introduction of thiokol leads to an improvement in the technological properties of BNR-based compositions, and also contributes to an increase in elasticity, which is important for sealing materials. Thus, the introduction of thiokol is a promising method for improving the operational properties of BNR-based materials.