synthetic fibers are very useful to us tell me something i want to no tell something i dont know but i know but can not understand but none of ur bissness =P
natural fibres are more comfortable to wear then synthetic. Synthetic are cheaper to produce , longer lasting than natural but not so comfortable to wear.
Denim itself is not a fibre... Denim is a fabric which is mostly commonly made out of cotton fibres (which are natural). However today much more denim is being made from a cotton-synthetic fibre mix.