Strathmore's 400 Series Mixed Media is a heavyweight, 140 lb (300 gsm), acid-free paper that combines the attributes of a watercolor paper with a vellum drawing finish.Ideal for wet and dry media, these cards accept watercolors, gouache, acrylics, graphite, pen-and-ink, colored pencils, markers, and collage. Cards: 140 lb. (300 gsm) Envelopes: 80 lb.(118 gsm)