The first synthesis of a polyurethane by frontal polymerization has been successfully carried out. Namely, the two reactants (1,6-hexamethylene diisocyanate and ethylene glycol) and the catalyst (dibutyltin dilaurate) were mixed together at room temperature in the presence of an additive (pyrocatechol, necessary for extending pot life), dimethyl sulfoxide (as the solvent), and a filler (fumed silica, added for stabilizing the propagating front). The reactions were thermally ignited at one end of the tubular reactor, and the resultant hot fronts were allowed to self-propagate throughout the reaction vessel. The effects of relative amounts of the above components on the most relevant parameters relating to frontal polymerization (temperature profile, front velocity, and temperature) were thoroughly investigated.