Hearing aid should be maintained in order to function properly. This maintenance also concerns replacing of certain wear parts such as tubes for a hearing aid. By wearing the hearing aid tube degrades, changing its physical properties and becomes hard and useless. It is assumed that one of the main causes of this degradation could be the heat of the human body and therefore, it is interesting to carry out research on the subject. Tube samples were heated at temperatures of 90 ° C and 120 ° C for different periods of time. Then, the analysis of samples was made by infrared spectroscopy to identify the type of polymer material and to investigate changes in the structure of the polymer caused by thermal aging. Swelling experiments were done to get more insight into the structural changes. IR spectroscopy indicates that the polymer from which the tube of a hearing aid is made, according to its chemical structure, is similar to polyethylene terephthalate. Spectra showed the presence of C = O, C-C (= O) -C and C-O-C group in the structure of the studied polymer and this fact supports the assumption that the investigated polymer is similar to polyethylene terephthalate. IR spectra also indicate the presence of OH groups in the thermally aged samples, as a result of the loss of the amount of these three groups. The IR spectrum of thermally degraded tubes showed a much weaker intensity of the peaks for C-O, C-C (= O) -C and C-O-C group and therefore, it can be concluded that the loss of these groups is caused by curing the tubes used for audio-waves conduction in the hearing aids. The effect of thermal aging on the loss of these groups is relatively small, so it is logical to suppose that the impact of heat might not the main cause of degradation of the tubes. The degree of swelling decreases slightly with the extension of the time of exposure of samples to the thermal aging at a temperature of 90 ° C, indicating a possible crosslinking of the polymer chains. However, this crosslinking is not strong enough to argue that the thermal ageing is the main cause of the material degradation. In contrast, heating at 120 ° C causes chain scission and softening the tube, followed by an increasing in the degree of swelling.