Grand Palace and Royal temples in Bangkok as well as Bang Pa In Summer Palace in Ayutthaya are the place of reverence for Thai people. 

Therefore, inappropriate clothes for entry into the Grand Palace and temples are as follows :

* No sleeveless shirts
* No vests
* No short top
* No see through tops
* No short hot pants or short pants
* No torn pants
* No tight pants
* No bike pants
* No mimi skirts
* No pants skirts
* No sleeping suit

List of Royal temples that required appropriate clothes :

* Wat Phra Kaew 
* Wat Pho 
* Wat Arun
* Wat Trai Mitr
* Wat Sraket  
* Wat Ratchanadda 
* Wat Suthat Thepwararam
* Wat Ratchabophit

Resource : https://www.royalgrandpalace.th/en/visit/practical-information