Cotton, avoid synthetics they dont breath well. When I travel to Thailand I pack cotton tee shirts ,shorts material does not really matter but I prefer denim. pants are not needed unless your going somewhere fancy ,maybe a nice 50/50 blend hawaiian shirt to go to nicer places.

You can certainly wear t-shirts in Thailand for everyday activities like shopping, dining, and exploring cities, but there are strict exceptions for religious sites. In 2026, Thai culture remains conservative regarding sacred spaces. When visiting any Buddhist temple (Wat), your shoulders and knees must be covered. A standard t-shirt is acceptable because it covers the shoulders, but tank tops, sleeveless shirts, or "muscle tees" are strictly prohibited. For men, a t-shirt and shorts are generally fine for most temples, though "Royal" temples like the Grand Palace require long trousers. For women, a t-shirt is great, but it should not be cropped or see-through, and must be paired with a long skirt or "elephant pants" that cover the knees. In 2026, many temples have moved toward digital monitoring or strict gatekeepers who will require you to rent or buy a sarong if your attire is deemed "inappropriate."