The heat pulse experiment is a well-known method for determining thermal
diffusivity. However, neither the measurement nor the evaluation methodologies
are straightforward for heterogeneous, highly porous materials. In the present
paper, we focus on two open-cell carbon foam types, differing in their porosity
but having the same size. Recent experiments showed that a non-Fourier
behaviour, called 'over-diffusive' propagation, is probably present for such a
complex structure. The (continuum) Guyer-Krumhansl equation stands as a
promising candidate to model such transient thermal behaviour. In order to
obtain a reliable evaluation and thus reliable thermal parameters, we utilize a
novel, state-of-the-art evaluation procedure developed recently using an
analytical solution of the Guyer-Krumhansl equation. Based on our observations,
it turned out that the presence of high porosity alone is necessary but not
satisfactory for non-Fourier behaviour. Additionally, the mentioned non-Fourier
effects are porosity-dependent. However, porous samples can also follow the
Fourier law. These data serve as a basis to correctly identify the
characteristic heat transfer mechanisms and their corresponding time scales,
which altogether result in the present non-Fourier behaviour. Keywords: flash
experiments, non-Fourier heat conduction, highly porous carbon foams