1. Make lightweight fabrics your friend.
Dressing to stay cool isn't only about less fabric—it's also about the type of fabric. Our experts recommend forgoing synthetic fibers for natural fabrics—which absorb moisture and allow air to pass through to your skin—whenever possible. Translation: Instead of polyester, nylon, rayon and acrylic, look for cotton, poplin, seersucker, linen and even summer-weight wool. "Anything that 'breathes' is going to be your friend," Kopulos said. "I feel like an 80-year-old woman saying that, but it's true." Also look for looser silhouettes that won't stick to your skin—one exception being moisture-wicking synthetic-performance fabrics that will help keep you cool, even if they fit more tightly. Bamboo-blend fabric is becoming more popular, and it's a warm-weather winner because it's both sweat-absorbant and antimicrobial, meaning it resists bacteria that make sweaty clothes stink.
2. Ditch the dark colors.
It may seem obvious, but many people overlook it: As much as you may love black, it's not doing you any favors during the summer months—and neither are brown or navy, for that matter. Whether you're dressing for work or playing outdoors, opt for white, beige, taupe and other colors that reflect light rather than absorb it.
3. Don't sweat it.
The darkest and lightest colors win when it comes to hiding inevitable (and icky) sweat spots. So we lied when we said black isn't doing you any favors. While it may cause you to sweat more than other colors because it absorbs sunlight, it redeems itself slightly by not showing said sweat. Still, whites and pale shades that keep you cooler and hide sweat are win-wins. Bright colors, which show a darker version of themselves when wet, are a gamble. The worst color you can wear? "Gray," Kopulos said. "It's the all-time most awful." Some prints can also help hide sweat spots.
4. Learn to love layers.
When you're going in and out of air conditioning and transitioning from hot days to cool evenings, layering is an essential survival tactic. For women, wear a sleeveless shirt or camisole when you're commuting or window shopping. Then throw on a blazer or sweater when you walk into your office building or a store, and take it off again when you meet your friends for happy hour or dinner. Added benefit: A bright tank can give you a pop of color that's a nod to the color-blocking trend, Coxworth says. Multi-purpose items work the same way. For guys heading to Millennium Park after a casual Friday at work, for example, Capo recommends a linen or cotton-linen-blend pant with an inverted zipper at the knee, which easily can be converted into cargo shorts.
Erin Gibbons is a RedEye special contributor.