The most common clothing textile trends for summer tend to be made of lightweight textiles including cotton, rayon, and linen. In a study evaluating the UV transmission of summer clothing in Switzerland and Germany in 2000 by Dummer et al, over 80% of summer textiles tested were made of cotton. According to this study, over 25% of the textiles tested under a UPF of 15, another quarter in the 15 to 25 range, another quarter in the 25-40 range, and only 25% tested over a UPF of 40. (Dummer R, 2000).
Cotton, depending on the type and construction of the textile, is lightweight and highly breathable. Although cotton is a commonly sought summer textile, many types of cotton can absorb sweat and holds it in the fabric. The fabric is touted to “breathe” when it's dry but when it's wet with sweat it can start to feel uncomfortable as it holds the moisture in the fabric. There are studies that show that people with eczema or atopic dermatitis favor lyocell. It tends to cause less itching, it is softer and it can regulate temperature and moisture more effectively than cotton. The cotton fiber itself is inelastic with 90% made up of cellulose. The rest of the fiber is made up of pectins, proteins, sugars, and organic acids. It is highly water absorbent and breathable. The inherent UPF of untreated cotton garments ranges from 1.6 to 13 based on a number of studies in the literature. To increase the UPF but maintain breathability, having an additional spandex element to the composition helps. Our studies that are supportive of our patent pending textiles have narrowed this range of spandex to the ideal composition to achieve both sun protection and maintain breathability.
Linen is often sought after for summer months due to its high breathability. From a sun protection point of view, it is very difficult to achieve higher UPF given the nature of the fiber and the loose composition of textiles.
I have studied bamboo with regard to sun protection as many companies tout the natural UV-blocking tendency of bamboo without backing up this claim. Bamboo is often even cited on skin cancer awareness sites for its “natural” tendency to block UV. However, the actual measured UPF of undyed knit 100% bamboo has a UPF of 13.861 in studies I have come across. To truly achieve sun protection the construction of the textile is key since if it is loosely knit or woven, the porosity will allow UV through. Bamboo is a natural fiber made up of cellulose, hemi-celluose, and lignin-derived from the bamboo culm. It is considered a bast fiber similar to jute or hemp. Bamboo manufacturing can be either mechanical or chemical. The mechanical process involves enzymatically breaking down bamboo and combing out its fibers but is not commonly used given its costly and labor-intensive properties. The more common process of extracting bamboo fibers is via the chemical process which is almost identical to the production of rayon utilizing carbon disulfide.
I encourage people to also consider compositions of polyester and recycled polyester for the summer simply because of their breathability and moisture-wicking properties. As a dermatologist, I come across “sweat acne” and “yeast folliculitis” on a daily basis due to poorly chosen garments that absorb and hold sweat close to the skin. Performance polyester can achieve sun protection and moisture wicking along with maintaining breathability.