Do I really need a rain jacket?

No. It is too humid. If it rains, buy a cheap plastic poncho for 20 baht at any convenience store or embrace getting wet; it will be warm anyway.

Don't overpack. There are 'wash and fold' services on almost every street in Thailand. Expect to pay about 40-60 baht per kilogram, and you'll get your clothes back clean and folded within 24 hours.

How to Pack for Hot Weather in Thailand

Pack lightweight, breathable natural fabrics like linen or thin cotton and limit your load to a 40L backpack to stay mobile. You need to dress modestly for temples, so always carry a lightweight sarong or oversized linen shirt to cover your shoulders and knees.

Choose your fabrics. Avoid synthetics like polyester, which trap heat. Stick to linen, hemp, or lightweight 'travel' cotton that wicks moisture and dries quickly after a monsoon shower.
Prioritize modesty coverage. Temples require covered shoulders and knees. Pack one pair of loose-fitting trousers (elephant pants are cheap to buy locally) and one light, long-sleeved shirt specifically for temple days.
Select your footwear. Bring one pair of reliable, water-friendly walking sandals and one pair of lightweight, breathable sneakers. You will be taking your shoes off constantly to enter buildings, so avoid complex laces.
Manage your liquids. Bring a high-quality solid shampoo bar and deodorant stick to save space in your 100ml TSA-compliant bag. Buy sunscreen locally at 7-Eleven; it is cheaper and specifically formulated for the local humidity.

Do I really need a rain jacket?: No. It is too humid. If it rains, buy a cheap plastic poncho for 20 baht at any convenience store or embrace getting wet; it will be warm anyway.
How do I do laundry?: Don't overpack. There are 'wash and fold' services on almost every street in Thailand. Expect to pay about 40-60 baht per kilogram, and you'll get your clothes back clean and folded within 24 hours.