Although there has been a lot of work on ignition times at constant imposed heat flux and on steady creeping flame spread, no definite results exist for the effect of material thickness on these phenomena, specifically away from purely thermally thick or thermally thin conditions. In this work, we first demonstrate, concentrating on the thermal ignition regime, that creeping flame spread can be cast in the form of ignition time at constant heat flux if surface heat losses are neglected. Subsequently, we review relations for ignition time for thermally thick, intermediate and thermally thin conditions including the effects of critical heat flux and heat losses. Finally based on these analyses we present for the first time, new nondimensional correlations and a theoretical way to include the effects of material thickness on creeping flame spread in a practical way as derived from exact equations in the ignition analysis. Then, we compare and validate the new relations using an earlier semi-empirical correlation developed by the author based on numerical and experimental data as well as with recent data.