Steam quickly heats and moistens the fibers in wood so it may be bent with out cracking. Heating the resin or sap has nothing to do with the process.
Wood may also be bent by soaking in water for a few days... Native Americans built their canoes this way. Unfortunately, the excessive water sometimes weakens or damages the wood. Another popular method of wood bending is to cut the wood into thin strips and glue the layers together while been held in the desired shape by a clamping jig. I have always noticed a little spring back after making a piece so I over compensate the bend by building the clamping jig to make a slightly sharper bend than needed. Brant Hollensbe West Des Moines, Iowa Bhollensbe at mchsi <wood that they want to bend. The heat softens the sap/resin in the wood so there is not much spring back if the softened wood is placed into a jig and left for the sap/resin to reharden or normalize.>