This work presents a thorough study on the Amide III band in fibrous proteins using Fourier Transformed Infrared Spectroscopy (FTIR). Type I collagen was chosen as a model for this family of proteins, not only because of its important role in mammalian tissues, but also for its involvement in several pathologies. In order to disclose the conformational information contained in the collagen bands, the spectral characteristics of Amide III of type I collagen were related to the ones of Amide I band, performing experiments of thermal denaturation of the protein in acidic solution. Data acquired allowed to observe the protein unfolding and retrieve information about its structural arrangements during the thermal cycle. Taking as guideline the well-known behaviour of the Amide I band, we correlated the structural changes deducible from Amide I analysis with the ones detectable for Amide III band, by exploiting three spectral analysis techniques, namely 2D-correlation analysis, second derivative analysis, and peak-fitting. This approach enabled us to jointly support the obtained results and finally to assign the components of the Amide III of a typical fibrous protein, such as type I collagen, to its characteristic secondary structure.