The tensile strength and binding properties of paper have been thoroughly investigated for the past 50 years. However, recent studies have shown that the binding mechanisms of fibers are not as clear as previously thought. Particularly, a paper by Hirn and Schennach  made a successful effort to quantify the contributions of different binding mechanisms. However, the uncertainty of the area in molecular contact, necessary for all molecular interactions but especially for interdiffusion, leaves an unwanted margin of error on the results. Therefore, determining the area in molecular contact is essential to perceive what holds the bond together in its inmost fold. For this purpose, we investigate fiber-fiber joints by Förster resonance energy transfer microscopy (FRET). This method is based on the dipole interaction of two dyes which are being covalently bound to the individual fiber surfaces. The dyes on the fibers (donor dye on fiber 1 and acceptor dye on fiber 2) are being excited by incident light of a certain wavelength. If the two fibers are close together (~1-10 nm) during this process, a part of the energy transfer between the chromophores happens non-radiative through a so called Förster transfer. Since the intensity of the emitted light of this interaction is proportional to the inverse sixth power of the distance of the two dye molecules it can be used to measure the distance between the two chromophores. This distance then corresponds to the distance between the two bonded fibers. In this work the area of molecular contact has been measured by FRET and polarized light microscopy. Since penetration of the dyes into the fibers can be a major cause of error fiber cross sections were investigated too.