Matrix transformer exhibits characteristics that can create low winding loss in high current application. The impact of multiple interleaving structure, the number of layers, and copper volume to winding loss are analyzed in this work. Compared to the 2D analysis, the 3D FEM analysis shows an increased AC resistance, due to the not captured proximity effect in part of the winding window. As a consequence, more copper will increase the AC resistance. This fact is often overlooked in matrix transformer design and can change the design result.