The Lahdenperä Fingerjoint surpasses the most demanding expectations Lahdenperä Fingerjoint technology allows us to provide material that conserves the environment, saves raw material and as a result saves costs. Using fingerjointed material, long pieces of wood become more stable, therefore preventing twisting and warping. VTT - The Technical Research Centre of Finland checks the high quality of our window and outside door products. In our opinion, doors, windows, stairs, and cleats are elements of décor in the home and are a matter of personal preference; every end-user sets his or her individual requirements. Thus, we feel it is important for us to pay attention to different customer qualities; for example, our products can be without knots on one or more sides. A well-manufactured Fingerjoint product will have tight fingers with an almost unnoticeable joint on the face and needs no sealant; only a straight butt seam is visible. Qualities: