2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/11387The properties of thermal material coexisting with non-thermal emitting plasma and strong magnetic field in the powerful jets of Active Galactic Nuclei (AGN) are examined. Theoretical and observational constraints on the physical properties of this `cold' component are determined. While the presence of a thermal component occupying a fraction ~1.E-8 of the jet volume is possible, it seems unlikely that such a component is capable of contributing significantly to the total jet energy budget, since the thermal reprocessing signatures that should appear in the spectra have not, as yet, been detected.12 pages, Latex (MNRAS format), 3 encapsulated postscript figures; revised version, submitted to MNRASAstrophysicstext