The minimum propagating current, the velocity of propagation, and the temperature rise in semistabilized superconducting wires with and without insulation have been measured by heat pulse tests in magnetic fields up to 70 kG. These experiments have shown that insulated wire can be more stable under external heat perturbation than bare wire and that its temperature rise after quenching is slower. The tests also show that the velocity of propagation is strongly affected, at any current level, by the cooling conditions and by even a very thin surface coating on the wire.