what is the difference between a 'poly belt' and a 'v drum belt' ?

i have an indesit w123 and the belt has worked slack,so i need to purchase a new belt because im sick of putting the existing one back on. have the belt details but i went on to a website to purchase the belt and i dont know if its the correct one as they only list the belts as poly belt or v drum belt can you tell me the difference between them beforwe i purchase?