The inverse photopyroelectric technique (IPPE) was adapted for the measurement of the thermal effusivity of resins during isothermal curing. The pyroelectric sensor consisted of a 9 mu m PVDF film heated by a modulated laser beam and coated with a thick layer of uncured epoxy. From the high frequency part of the pyroelectric spectra of this bilayer the sensitivity of the pyroelectric detector was determined, while from the low frequency part the sample's effusivity (c rho k)/sup 1/2 / was found. The isothermal crosslinking of an DGEBA-based epoxy with DDM was studied at cure temperatures between 38 and 60 degrees C. The thermal effusivity shows a marked increase until it drops when the rubber to glass transition is passed, i.e. when the network formed vitrifies to its glassy state. Concurrent results from modulated differential scanning calorimetry (MDSC) showed that the increase in the effusivity by up to 30% is mainly caused by the increase in thermal conductivity due to the crosslinking, while the stepwise decrease should be attributed to the drop in specific heat. Further consideration of the frequency dependence of the vitrification time obtained by IPPE-, MDSC- and dielectric studies confirmed that the same dynamic process, viz. vitrification, is monitored with these different techniques.