The mechanical strengths of polymer composite (PC) are influenced by techological manufacturing parameters, technical parameters of reinforced materials and polymer matrix. To determine optimal technological parameters of manufacturing PC, reseachers have to do a lot of experiments for a long time. At present, application of experimental plan permits to reduce the number of experiments but to keep the experiments precisely. The article presents Box-Wilson experimental plan supported by Design-Experts sofware to do a reseach on simultaneous influences of manufacturing parameters: temperature of curing, pressure and fabric/resin's mass percentage on the mechanical strengths of PC based on phenol-formaldehyde reinforced with cotton woven fabric. The reseach results specify optimal parameters of manufacturing PC including temperature 145°C, pressure 2.15 MPa and fabric/resin's percentage 55 percent with PC's maximum mechanical strengths: tensile strength 68.68 MPa, compressive strength 57.54 MPa, charpy impact strength 81 kJ/m2.