Abstract <p>Research works on the development of urethane-forming compositions and carbon- and glass-fiber-reinforced plastics based on them obtained by vacuum infusion are continued. A laboratory thermovacuum infusion unit is created. Prototype samples of such composites are obtained and tested. Correlations between the qualitative indicators (viscosity, hydroxyl number (HN)) of component <i>A</i> in polyurethane (PU) binders and between the HN and physical and mechanical indicators of cured binders are found. It is shown that the dependences of the strength and Young modulus of PU films increase with increasing values of the HN and have an exponential and polynomial character of the dependence. An attempt is made to find explanations for the observed phenomena. It is found that the same regularities are observed on the composites as on PU films: the physical and mechanical indicators of carbon- and glass-fiber-reinforced plastics increase with an increase in the values of the HN.</p>