Cotton, silk, flannel … or your birthday suit? What to wear for a great sleep.

When you slip beneath the sheets, what you're wearing counts.

The feel and fit of your sleepwear can make all the difference in how you sleep.

"Besides the comfort and fit factor, just the psychological act of changing out of your work clothes helps ready your body for sleep," says registered nurse Terry Cralle, a certified clinical sleep educator in Washington, D.C.

If you roll into bed in the same loungewear you've been wearing watching Netflix all afternoon, you can have problems transitioning into sleep, she says.

Since studies suggest that sleep is strongly affected by heat and cold, you'll also want your pajamas to keep your temperature just right.

Here's the scoop on five of the most popular nightwear options:

Cotton

It's been around for so long so many people are comfortable with cotton, says Haralee Weintraub, CEO of Haralee.Com, which specializes in moisture-wicking sleepwear. Easy to care for, it's durable and soft. But if you suffer from night sweats, cotton may not be your best choice. Cotton is absorbent and tends to hold onto water — just think of those thick cotton bathroom towels. If you already have insomnia, getting up to change out of wet garments in the middle of the night may not be the best use of your zzz time.

Silk

Cralle says that silk is good at thermoregulation, keeping you warm when you're cold and cool when you're hot. Silk may be slinky, but it doesn't always play well with satin-type sheets. If you toss and turn, the combination may prove slippery enough that you'll wake and miss out on a full night's sleep, she warns. "Silk's higher price tag and need for delicate handling may not make it the most practical choice for everyday sleepwear," adds Weintraub.

Flannel

Warmth and breathability are two qualities of this soft material, which is also strong and durable and can keep you feeling comfortable without overheating. Similar to other fabrics, flannel can be blended with other materials — a flannel-polyester blend or 100 percent brushed flannel is used for sleepwear, says Weintraub. If you're always cold, flannel could be just what you need to keep you cozy. But if you like to sleep with lots of covers or a heavy quilt, sleepwear made of flannel might heat you up a bit too much, says Cralle.

Bamboo

Fabric made of bamboo fibers is hypoallergenic and it may be good for those who suffer from allergies. This soft and silky fabric is 100 percent biodegradable. Weintrab says bamboo is also good at wicking moisture, another good choice for hot sleepers.

Polyester

Once thought of as cheap and uncomfortable, newer technology has made polyester more desirable, especially when blended with other fibers like cotton or rayon, which increase its softness and durability, says Weintrab. She likes polyester for its moisture-wicking properties.

Au Natural

Since science (like this article in the Journal of Physiological Anthropology) says that you sleep better when your body is cool, for those who prefer skin-to-sheet contact, sleeping sans bedclothes might be an effective, alternative way to keep your body temperature down and your sleep quality up.

Sleeping in your birthday suit may be that perfect gift: A good night's sleep.

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