Non-adiabatic pressure perturbations naturally occur in models of
inflation consisting of more than one scalar field.
The amount of non-adiabatic pressure present at the end of inflation
can have observational consequences through the generation of
vorticity and subsequently the sourcing of B-mode polarisation.
In this talk I will give an overview of adiabatic and non-adiabatic
inflationary models and describe our recent calculation of the
spectrum of isocurvature perturbations generated at the end of
inflation for different inflationary models which have two scalar