Cambodia is quickly embracing the 21st Century and very accepting of tourists however it is still a deeply conservative nation with strong beliefs about modesty. So the suggestion is to think twice before packing your suitcase. The question isn't just: what's weather appropriate, but what's culturally appropriate.

Men.  For general touring about the temples and daytime walking around town, shorts are more comfortable than long trousers, but be careful about insect bites (those tiger mosquitos pack a punch) and sunburn.  Most local guys wear trousers rather than shorts. At night, or at any place remotely formal (a temple, visiting a home, a business meeting) shorts are really not appropriate, though locals are too polite to comment. It may pay to pack not just shorts and jeans, but also a slightly conservative pair of trousers that don't scream "cargo pants."

T-shirts are commonly worn by locals and visitors but again for any occasion remotely formal or where showing respect is required, locals will wear long or short sleeved button-up shirts.

Women. Many female tourists react to the hot temperatures by going around in spaghetti-strapped tops. These are considered risque or simply disprespectful and locals are frankly offended by such disrespect - though again will generally be too polite to comment. In the countryside, or when visiting temples or people's homes, wear a t-shirt at least, or blouse.

Skirts or jeans? Again, in more formal settings or when you are visiting a home or temple, think "somewhat conservative" and wear a dress or skirt. When out doing day trips by tuk tuk, then you can dress more casually.

The next consideration is temperature. With temperatures typically in the low to middle 30s, cotton trumps synthetics, but be prepared to have two or even three changes a day. Typical strategy: a morning outfit, come back to the guest house at midday, have a shower, get changed and get ready for the afternoon. That will mean lots of changes of clothes on a two week journey, so consider your laundry needs. Local services clean laundry at $1 per kilo of laundry (next day delivery) or be prepared to wash undies and t-shirts in the sink at your guest house room.

Footwear.  TEVA open sandals are ideal for exploring temples in: and their slip-on/slip-off quality is handy when you need to take shoes off at the door.  For the same reason, high-top sneakers can be a real pain. (Same at the airport.)  For more formal occasions (business meeting, restuarant etc) then normal closed shoes are more idea. Rubber flip-flops are good for wearing inside your hotel/ guest house room if you don't like going barefoot.  In wet seasons it pays to have more than one set of footwear, just in case the TEVAs end up getting super soggy (or muddy) while out exploring.

Summary:  Do think about culture. After several journeys to Siem Reap, this writer has heard many times from locals how they really feel about immodest dress. It may suit the tropical climate, for sure, but it reflects poorly on the sensitivity of the wearer. Show respect.