Thai wedding attire can be a silk wedding dress or traditional handwoven cotton or even made of modern synthetics. There is no right or wrong just a matter of choice and personal style.
Younger brides often choose synthetic materials as they have a great range of colors and designs then traditionally handwoven cotton or silk Thai wedding dresses. "That is the tradition of Thai wedding dresses, they where always influenced by modern trends" So what ever you choose for your Thai wedding dress is acceptable. Well almost anything! There is no rules except Thai custom does not allow black attire at weddings, as it is considered to be bad luck.
See here for Thai wedding dresses.