I have two kinds of cotton right now. The first is sterile CVS cotton - no boiling needed. It does impart a very mild cottony taste right as the juice vapes away. Not much though. The second is an organic cotton grown with no pesticides. It does not impart any flavor (even without boiling) and is made for skin care, but it is not as absorbent as other cotton. It also leaves an odd feeling in my throat - again, only on the last hit when the juice is about gone. Both work reasonably well in a RDA (I have a Trident) and are much better than other wick materials, but I am really ready to expand my vaping experience and venture into the world of gennies.
Try boiling them. I boil my organic cvs cotton balls, because before I tried that they had a slight cotton taste and left a bad feeling in my throat. Despite being organic they are bleached with hydrogen peroxide, so there is most likely still some left over from the process. My bag had a faint peroxide smell.