Sunlighten’s recommendation to wear natural fibers like cotton when using the sauna is based on two main factors: the science of infrared absorption and the safety of the air you're breathing.

Why Avoid Synthetic Clothing?

Synthetic fabrics (polyester, nylon, spandex) are essentially forms of plastic. In an infrared environment, they create several issues:

• Infrared Reflection/Blocking: Infrared heat works by penetrating the skin. Synthetic fibers are often more "reflective" or dense at a molecular level than natural fibers. They can act as a thermal insulator, blocking the infrared rays from reaching your body and essentially turning your high-tech sauna into just a "warm room."

• Off-Gassing: Because infrared saunas heat objects directly, synthetic fabrics can reach temperatures where they begin to "off-gas." This means the chemicals and dyes in the plastic-based fibers can release trace Volatile Organic Compounds (VOCs) into the small, enclosed cabin. Since many people use saunas for detoxification, breathing in heated plastic fumes is counterproductive.

• Bacteria & Skin Irritation: Synthetics trap moisture against the skin rather than absorbing it. In the high-heat, static environment of a sauna, this creates a "plastic wrap" effect that can lead to skin irritation, rashes, or trapped bacteria.

Why are Bathing Suits "OK" if they are synthetic?

This is a common point of confusion. Most bathing suits are made of polyester or nylon, so why are they allowed?

• Surface Area: The "as little as possible" rule is king. A bikini or small swim trunks cover very little skin, allowing the infrared heaters to reach 90% of your body. The small amount of synthetic material is considered a "tolerable" trade-off for modesty in a public or guest setting.

• Hygiene & Practicality: Swimwear is designed to get wet and dry quickly. In a commercial or shared setting, it’s a standard requirement for hygiene.

• The "Lesser of Two Evils": Wearing a full synthetic tracksuit is a major "no" because of the large surface area off-gassing and blocking heat. A small swimsuit has a negligible impact on the overall air quality and heat absorption compared to full-coverage clothing.

Why Loose Clothing instead of tight clothing?  

The recommendation for loose-fit natural clothing rather than tight-fitting garments (like compression gear or tight leggings) comes down to how your body regulates heat and how infrared energy interacts with your skin.

•  The "Boundary Layer" & Evaporative Cooling: The primary way your body stays safe in a sauna is through evaporative cooling (sweating).

• Loose Clothing: Allows air to circulate between the fabric and your skin. This airflow helps sweat evaporate, which is the mechanical process that actually cools your core temperature and prevents you from overheating too quickly.

• Tight Clothing: Traps a thin layer of moisture directly against the skin. Once that layer becomes saturated, your "cooling system" stalls. This can lead to a rapid, uncomfortable rise in body temperature and skin irritation.
  

• Infrared Penetration: Infrared heat is "radiant" heat—it wants to travel in a straight line from the heater to your body.

• Loose Clothing: Moves as you move, creating "windows" for the infrared light to hit your skin directly.

• Tight Clothing: Creates a constant, solid barrier over 100% of the covered area. Even if the fabric is cotton, the density of a stretched, tight fabric can slightly decrease the efficiency of the micron-wavelength penetration compared to bare skin or a loose-draping garment.
  

• Lymphatic Flow and Circulation: One of the major benefits of a Sunlighten sauna is increased circulation and lymphatic drainage. Tight elastic waistbands or compression tops can restrict superficial blood flow and lymphatic movement.

  The Goal: You want your vessels to vasodilate (expand) fully. Loose clothing ensures there is no external pressure "squeezing" your tissues, allowing for maximum blood flow to the surface of the skin. As you sweat, your body is pushing out salts, oils, and metabolic byproducts. Loose Cotton gently wicks these away and allows the skin to "breathe.” Tight Clothing effectively "pastes" those excreted toxins back against your pores. This can lead to folliculitis (clogged hair follicles) or heat rashes, as the debris has nowhere to go until you peel the clothes off.

Sweat levels are different for everyone. Don’t be surprised if you don’t sweat during the first few sessions. Sweating will increase with regular use. Even if your body is not drenched in sweat, your body is still detoxifying from harmful toxins. Also, be sure to drink plenty of water before your session. If you are dehydrated, you will not sweat as much.

No. The infrared heat comes from specialized heating panels built into the floor, front, back, and side walls. Infrared wavelengths are completely invisible to the eye.

Yes, the sauna is still working. Infrared heat waves bypass the air to  penetrate your body directly rather than relying on visible light to warm the space. That means you don’t need a visible glow to get the physical benefits. The red lights you see are for red light therapy, an additional therapy integrated into your sauna experience and may cycle on and off throughout your session.  You also have the option of utilizing Chromotherapy as well.  Read more about Chromotherapy in another section of the guide.