We studied the effect of morphological variation and basking posture on thermal characteristics in the speckled wood butterfly Pararge aegeria (L.). The process of heating and cooling in relation to wing type (descaled, darkened and original wing colour) and size was examined using dummies (i.e. dried butterflies). Size (measured as wing length) and ambient temperature have a joint influence on body temperature: large butterflies heat up more slowly than small ones, but with increasing ambient temperature the difference with size became smaller and even changed since large individuals heated up faster under warm ambient conditions. Surprisingly, darkening wings had no overall effect on thermal characteristics, but this may be an artefact of the manipulation as supported by the results of the absorption measurements. Normal butterflies reached a higher equilibrium thoracic temperature than descaled butterflies probably because wings without scales absorb less radiation. Finally, butterflies with fully spread wings reached higher thoracic temperature and had faster cooling rates compared to butterflies with half-opened wings. Implications of the results for the relation between morphology and behaviour of speckled wood butterflies in their natural habitat are discussed.