F1, F2, and F3 all show a shallow gradient at temperatures below T g, as well as above T g,↵ (shown in Figure ). Previously we have always observed an increase in terahertz absorption with temperature above T g,↵ for a wide range of less complex organic molecular materials due to their steadily increasing molecular mobility . We hypothesise that in these systems the local conformations of the BSA molecules become trapped in the matrix by energy minima that are relatively more stable than kT . As a result, the motions of the most flexible domains of the BSA molecules and their matrix become restricted. Such confinement reduces the flexibility and hence molecular mobility of the protein and matrix molecules. A plateau in terahertz absorption at high temperatures could therefore be interpreted as a molecular confinement of the protein in its surrounding matrix.