If you put a towel over a radiator is the heat energy wasted?

I'm no physicist but say, a radiator will give off some heat energy. If i put a towel over the radiator does it waste that heat energy by blocking it or does it just slow down the process of giving off the heat? What i'm asking is will the same amount of heat reach the air in the room eventually or does the towel prevent some of it from affecting the room temperature?