Pack for Heat
The best fabrics for tropical climates are lightweight and made from natural materials.
Pack light-colored clothing.
Darker colors absorb more light so they are going to keep you hotter.
Your body loses heat by the evaporation of sweat from the skin. High humidity and garments that trap sweat against your body hamper this cooling process which, in turn, allows your body to overheat. So -
01. Avoid Synthetic Fibers
Being water-repellent, they don't wick sweat away from your skin. Rather, they hold sweat under the fabric which reduces evaporation and sooner or later causes discomfort and irritation. Silk is also not a good choice as it also tends to retain moisture. And besides - sweat will eventually harm the material.
02. Choose Cotton
It is extremely comfortable and allows your body to breathe with ease and easily absorbs excess sweat. Linen and other natural fibers also breathe and are good at absorbing moisture. But choose your type of cotton wisely. Instead of wearing heavier versions of cotton such as twill, which is what your bluejeans are made of, opt for poplin, seersucker and madras cotton. Besides, bluejeans are heavy for packing and do not lend themselves to washing along the trip. Wash 'em at night - they're never dry by morning.
03. Check Out Wool
With its natural ability to breathe, wool is better than all polyester fabrics. Wool socks wick moisture from the feet helping to prevent blistering in hot weather walking. Changing socks every couple of hours while hiking is good advice. Avoid blisters at all costs.
04. Cover Up
Also, consider that clothing is the most basic form of protection against the sun. So opt for long sleeves and t-shirts that cover the sensitive area at the base of your neck if you will be exposed to the sun's harmful UV radiation throughout the day.
Wear one! Protect your scalp from sunburn. And if you wear a wide-brimmed hat, you can protect your neck as well. Vents in the hat will facilitate heat loss to keep you cooler. And - in addition to sunglasses, wearing a wide-brimmed hat on sunny days can reduce your eyes' exposure to harmful UV and High Energy Visible rays up to 50%.
06. Neck Coolers
Here is a Consumer Report Article on the subject. Seems a nice red bandana soaked in water and wrapped around your neck would do as well - particularly in a high humidity environment.
Bottom Line: Dress as the desert-dwelling people have for centuries with lightweight, loose-fitting, sun-shielding body coverings from head to toe.