Method for the production of urea-formaldehyde resins, characterized in that it comprises: a) a methylolation step, comprising: - loading formaldehyde and, optionally, water, into a reactor equipped with stirring, cooling and heating; wherein formaldehyde refers to formaldehyde, paraformaldehyde and/or UFC (Urea Formaldehyde Concentrate), or a mixture thereof; - adjusting the pH between 4.5 and 5.5; - adding urea, in an amount such that the molar ratio of formaldehyde/urea is between 5.2 and 4.8; - carrying out the methylolation reaction, maintaining the pH between 4.5 and 5.6, at a temperature between 70 and 120 °C, during between 5 and 100 minutes; b) a condensation step, comprising: - adding urea to the reactor, in an amount such that the molar ratio of formaldehyde/urea in the reactor is between 2.5 and 1.5, adjusting the pH between 5.0 and 5.8; - heating to 70-120°C, in a range of pressure from 0.05 bar to 2.5 bar, during between 30 and 300 minutes, to carry out the condensation reaction; - plotting a condensation curve, measuring the viscosity of samples from the reaction mixture, at different time intervals during the condensation reaction, with a viscosimeter at 25°C, until the viscosity corresponding to the aimed molecular weight is reached; - finalising the condensation by adding an alkali, to obtain a pH between 7.1 and 8.5; c) a final urea addition step, comprising: - adding further urea, at a temperature of 70 to 30 °C, during 15 to 120 minutes, maintaining a pH between 7.3 and 8.8, to reach a final molar ratio of formaldehyde/urea between 3 and 0.5; - cooling to a temperature lower than 30 °C; wherein the pH is adjusted by adding an alkali or an acid as necessary, and is determined by use of a pH-meter. a) a methylolation step, comprising: - loading formaldehyde and, optionally, water, into a reactor equipped with stirring, cooling and heating; wherein formaldehyde refers to formaldehyde, paraformaldehyde and/or UFC (Urea Formaldehyde Concentrate), or a mixture thereof; - adjusting the pH between 4.5 and 5.5; - adding urea, in an amount such that the molar ratio of formaldehyde/urea is between 5.2 and 4.8; - carrying out the methylolation reaction, maintaining the pH between 4.5 and 5.6, at a temperature between 70 and 120 °C, during between 5 and 100 minutes; - loading formaldehyde and, optionally, water, into a reactor equipped with stirring, cooling and heating; wherein formaldehyde refers to formaldehyde, paraformaldehyde and/or UFC (Urea Formaldehyde Concentrate), or a mixture thereof; - adjusting the pH between 4.5 and 5.5; - adding urea, in an amount such that the molar ratio of formaldehyde/urea is between 5.2 and 4.8; - carrying out the methylolation reaction, maintaining the pH between 4.5 and 5.6, at a temperature between 70 and 120 °C, during between 5 and 100 minutes; b) a condensation step, comprising: - adding urea to the reactor, in an amount such that the molar ratio of formaldehyde/urea in the reactor is between 2.5 and 1.5, adjusting the pH between 5.0 and 5.8; - heating to 70-120°C, in a range of pressure from 0.05 bar to 2.5 bar, during between 30 and 300 minutes, to carry out the condensation reaction; - plotting a condensation curve, measuring the viscosity of samples from the reaction mixture, at different time intervals during the condensation reaction, with a viscosimeter at 25°C, until the viscosity corresponding to the aimed molecular weight is reached; - finalising the condensation by adding an alkali, to obtain a pH between 7.1 and 8.5; - adding urea to the reactor, in an amount such that the molar ratio of formaldehyde/urea in the reactor is between 2.5 and 1.5, adjusting the pH between 5.0 and 5.8; - heating to 70-120°C, in a range of pressure from 0.05 bar to 2.5 bar, during between 30 and 300 minutes, to carry out the condensation reaction; - plotting a condensation curve, measuring the viscosity of samples from the reaction mixture, at different time intervals during the condensation reaction, with a viscosimeter at 25°C, until the viscosity corresponding to the aimed molecular weight is reached; - finalising the condensation by adding an alkali, to obtain a pH between 7.1 and 8.5; c) a final urea addition step, comprising: - adding further urea, at a temperature of 70 to 30 °C, during 15 to 120 minutes, maintaining a pH between 7.3 and 8.8, to reach a final molar ratio of formaldehyde/urea between 3 and 0.5; - cooling to a temperature lower than 30 °C; - adding further urea, at a temperature of 70 to 30 °C, during 15 to 120 minutes, maintaining a pH between 7.3 and 8.8, to reach a final molar ratio of formaldehyde/urea between 3 and 0.5; - cooling to a temperature lower than 30 °C;