Optical fibers are usually protected by a loose tube formed by extrusion. The loose tube can consist of one or more plastic layers. In this paper, the thermal stresses in the dual layer loose tubes, which are caused by the inhomogeneous cooling at the end of the extrusion phase, have been calculated based on a numerical method. It was found that the thermal stresses in these loose tubes depend on the adhesion of the two layers and the ratio of the wall thickness between the two layers as well. In general, if there is a good adhesion between the two layers of the loose tube, higher thermal stresses are found in the inner layer.