A method of determining a deformation condition initially comprises forming a tractable product into a desired configuration. This product being one which is, or is a precursor to, a polymeric material having chains including Raman active bonds which are capable of stretching but not rotation and which provide at least one diagnostic band in the Raman spectrum of a frequency dependent on the deformation condition of the material. The Raman active material is preferably a copolymer having poly(diacetylene) chains in a hard segment phase. Raman excitation radiation is directed to said material and the frequency (or a representation thereof) of said at least one diagnostic band is detected. This value is compared with the value obtained for the corresponding band of the material in a reference condition. The deformation condition is determined from this comparison.
