<p>The following study investigated the modification of beech wood (<i>Fagus sylvatica</i>) by furfurylation and polyesterification as an alternative to traditional preservatives. The impregnation of beech boards was carried out on a pilot-scale impregnation autoclave using the following impregnation cycles: vacuum-pressure, pressure and vacuum processes. Furfurylation was carried out with a 45% w/w furfuryl alcohol solution in the presence of tartaric acid as catalyst, and polyesterification was performed with a citric acid–glycerol solution at 44% w/w. Vacuum-pressure impregnation recorded the highest weight gain for furfurylation and polyesterification treatments, followed by pressure and vacuum cycles. As the degree of modification is assumed to depend on the weight gain after treatment, the vacuum-pressure process resulted in a significant improvement of properties. With this cycle, high resistance to leaching, wood-destroying fungi and termite attacks were observed for furfurylated and polyesterified beech wood. Both treatments resulted in a high modification of wood mechanical properties, showing increased hardness, stiffness, anti-swelling efficiency, and reduced wettability. However, vacuum-pressure impregnation performed with both treatments resulted in a wood bending strength decrease of 17%, while pressure impregnation process preserved wood resistance to rupture. Overall, furfurylation and polyesterification performed with a vacuum-pressure impregnation process led to the development of a material with enhanced properties, suitable for outdoor applications.</p>