This paper considers the use of lignin during the preparation of phenol-formaldehyde resins. The effect of lignin on the properties of phenol-formaldehyde resins and materials based on them is studied. The obtained resins are characterized by differential scanning calorimetry (DSC). The results show that, in the case of increasing the concentration of lignin, the time of the polycondensation reaction, the energy of activation, and the curing time of lignin-containing resins increase. The main parameters of the lignin-containing resins correspond to GOST (State Standard) 20907–2016 except for the concentration of free formaldehyde. The obtained resins are used to obtain a foam composite material—phenolic foam. It is noted that phenolic foams based on resins containing 5–10% lignin in the composition have a higher compression strength in comparison with other samples. At a concentration of lignin in the resin of 20%, the compression strength of the ready-to-use thermal-insulation materials decreases relative to other samples, while it turns out to be impossible to obtain a foam material in the case of using a resin with 30% lignin. The results of the study make it possible to recommend the use of a small amount of lignin (5–10%) in the production of phenol-formaldehyde resins and further production of a thermal-insulation material with an increased compression strength.