J.  Cotton...turkish, egyptian, pima...doesn't matter as long as it's 100% cotton.  Can't stand those velour, micro-something bathrobes you put on after a shower and you never feel dry!  So spend a little more at the beginning and buy the most pure you can afford, wash them separately in hot, hot water (but no fabric-softener please, it inhibits absorbency) and they will last a lifetime and just get softer and softer and softer...