We've never been happy with the traditional nylon/Lycra® construction of most seamless base layers, which tend to hold a lot of moisture. We engineered this Core Seamless with a mixture of polyester and polypropylene that moves the moisture away from your body with absolutely minimal moisture uptake.
The fabric is soft next to your skin and provides great temperature regulation in mild conditions. It's not for hot temperatures but it does work as a first layer even into cooler temperatures, while the seamless construction keeps it extremely comfortable next to your skin.