16 x 20"
From the manufacturer:
This traditional interleaving material is translucent, acid-free, and unbuffered. Use glassine for a variety of conservation applications. The surface is very smooth and has a pH of 7.0. It's light weight makes it easy to fold yet it maintains its shape well. Often used for interleaving watercolor and charcoal drawings but is not recommended for long-term photographic storage.