Silk burns easily.
The Silk Shirt is the third-weakest clothes, providing +7 Defense, reducing Thunder damage by 50%, and teaching Cure and Thunder. It can be bought for 400 gil at Dali, Treno (disc 2), Lindblum (disc 2), and the Black Mage Village (discs 2/3), found in Alexandria from Brahne (disc 1) by impressing 80-99 Nobles during the play, or stolen from Steiner or Black Waltz 1.
The Silken Shirt is a low-ranked mystic armor that provides +6 Defense and +2 Magick. It can be bought for 300 gil at Rabanastre, Nalbina Fortress, and Bhujerba, and requires 20 LP and the Mystic Arm 2 license to equip.