This is a good question.
We at GoSikh.com, sell many types of Turban Material and I will list them by weight (lightest first):
F74 and Mul Mul are very close in weight but not in thread count. F74 has less thread count when compared to Mul Mul. Both are used for Dumalla.
Silk is used by very few folks and mainly used for special events. It is pure silk and thus more expensive compared to other materials.
Full Voile is the regular Turban material most Sikhs use.
Rubia is the heaviest of all material and is the same cloth used to make Patkas.
All materials marked with an "*" are made of 100% cotton.
If you are curious of what length of Turban should you choose, please read that blog entry further down. If you have any questions, email me, leaving a comment here might not get you a quick reply.