Why does silk have more lustre but cotton has dull appearance inspite of both being from natural fiber?

Question

i need the answer to complete my assignment

Answer 1

Well, frankly, it's the weave of the threads and the finish on the fabric.   I have had silk shirts that were not smooth and shiny at all, as they were woven with bumpy threads and no finish applied and I have had pima cottons that were done in fine threads and a shiny finish added to them.  Why is an apple shiny and a pear is not?  Different fruit, different peels.

Answer 2

even if both are natural they are still made from different materials (like a stone and a ruby) also the way each fibre is woven plays a role.