Solid state nuclear track detectors have been applied in different studies including nuclear physics, particle physics, archaeology etc. Makrofol, a particular group of thermoplastic polymers, is used for radon detection. High background track numbers in the foils cause big uncertainties for places where the radon concentrations are quite low. Therefore, it is of great importance to lower the background track signal as much as possible, without reducing the sensitivity of the foils. The present study reports track density and sensitivity of Makrofol-DE after thermal annealing. The unexposed foils were heated at temperatures ranging from 110 degrees C to 140 degrees C for 10 min with the aim of observing changes in the number of background tracks. As a result a reduction in the background track density was observed. In order to observe the change in the sensitivity, pre-heated and unheated foils were exposed to alpha radiation in a radon chamber. At the temperatures of 110, 120, and 130 degrees C, the track density in the heated and unheated exposed foils is quite similar. An increase was observed in the track density in heated exposed foils at 140 degrees C.