If you were to wear a common cotton sweatshirt vs a polyester bike jersey, how much difference in speed would you gain/lose from the cloths alone?What about skin? Just to nerd out about it.
It's not as much about cotton vs polyester as it is about fit and permeability. Loose fit jacket/sweaters that balloon out and flop about can have a noticeable effect. Reasonably tight will have no important effect at normal speeds.
I thought at first sight that the question was about breaking wind while cycling! That would make no difference beyond motivating the rider to speed away from anyone who heard and was laughing at them. Otherwise as John M said, unless you ride at pro athlete speeds air resistance from clothing will have no noticeable effect. The main advantages of specialist cycling clothing are for warmth and wicking away sweat.
not that much if you are not racing you will not notice the difference cycling clothes MIGHT be more comfortable i personally debate that i almost never wear cycling specific anything except gloves helmet and SPD shoes i get by just fine but i am not racing i just don;t believe in having 15 sets of special outfits, for all 4 seasons, particularly at $150 each so i decided not to do that almost everything i wear is 'wrong' yet i get through 5000 miles a year of useful trips and fun exercise wle
