In last decades sheep breading in Baltic region has developed. As the main products usually are mentioned wool, meat, leather, and milk. However, since lately the main focus is on the meat production, textile-quality wool selection is not performed, and wool becomes a troublesome and secondary by-product. Meanwhile the sheep shearing costs remain high [1]. Wool may remain in the farms and collection of wool may take place even a remarkable time after shearing. Nevertheless, even such fibers may be used for development of new wool-containing products, such as air filtration systems with incorporated wool and/or thermally processed wool. In order to estimate influence of storing conditions on fibers and effect on further processing, a long-term exposure of wool fibers under various pre-treatment, temperature, light, humidity and air presence conditions was performed, thermal properties and chemical bonds were analyzed. Thermal analysis performed with Seiko Exstar 6300 thermal analysis device, while chemical bonds analyzed with Bruker Vertex 70v Fourier transform infrared spectrometer. Infrared analysis show that the wool fibers contain chemical bonds characteristic to the keratin structures. Thermal degradation of wool takes place in several main steps, related to release of absorbed water, decomposition of ammonia and sulfur containing compounds as well as decomposition of C-H bonds. The obtained results show that wool fibers are comparably stable under light, temperature, and air presence, while humidity presence introduces changes in the chemical bonds of keratin structure.