In Sri Lanka’s heat the most practical and comfortable clothing is loose fitting, light cotton wear. This is applicable for most parts of the country as the weather is hot and humid. However the Hill Country is similar to an English spring with the temperature becoming colder in the night. In the mountains a good wool sweater is advisable for the nights while in the day time a jumper or light cardigan should suffice to keep the cold away.
In general travelers should stick to casual wear which gives you more freedom while you explore the country. Women can wear bikinis when they are on the beach but when travelling around they need to be mindful of cultural sensitivities, so generally knee length shorts/dresses/skirts are advisable. Sleeveless tops or t-shirts are also fine unless one is visiting a religious site.
Travelers need to be properly attired when visiting sacred sites and shrines as revealing items of clothing are frowned upon and entry into such sites may be denied. Women travelers will need to cover their shoulder and legs so it is good to have a light scarf and sarong at hand to wear when necessary. Men should also note that long shorts or trousers paired with t-shirts or shirts would be the preferred option at religious sites.
Sandals or flip flops are much more comfortable than shoes and when visiting temples or shrines they are easier to remove. However if planning on engaging in hikes up mountains or through jungle trails a good pair of socks and trainers would be the better option.
Sunglasses, hats or caps are also a necessity to protect you from the bright rays of the sun.