The thickness of the underlayment for engineered wood flooring will depend on the specific requirements of the manufacturer and the condition of the subfloor. In general, a standard thickness for foam or cork underlayment ranges between 2mm to 6mm. Thicker underlayment can provide enhanced sound reduction and cushioning. However, it is important to consult the manufacturer's guidelines and recommendations for the specific type and brand of engineered wood flooring being installed. Additionally, the subfloor conditions should be taken into account. If the subfloor has minor imperfections or unevenness, a thicker underlayment may help to create a smoother and more even surface. Properly selecting the thickness of the underlayment will contribute to the overall performance, comfort, and longevity of the engineered wood floor.