In a nutshell: The Tree Napper delivers airy, cooling comfort, while the Cotton Napper treads a perfect balance between breathable and cozy. The key difference comes down to the fabric. The Tree Napper is woven from a cool-to-the-touch, moisture-wicking fabric called Tencel. It gives off that ‘cool-side-of-the-pillow’ feel, and when coupled with our breathable, open-loop knit design, it really helps to keep you nice and cool all night long. While the Cotton Napper might not have the same cooling properties, the organic cotton we use is naturally breathable, and our breathable design keeps you cozy but comfy. A handful of our customers actually found the Cotton Napper too cool, so you never know – one person’s cozy is sometimes another person’s cool!