These rigid boards are made of 1/4" thick corrugated white plastic. They will provide a firm support and are extremely easy to clean. Excellent for stapling or taping watercolor paper to for painting in or out of the studio. Carrying handle makes them easy to take into the field, square shape allows setting up onto an easel. Made in half size for 15 x 20" sheets, mid size for papers up to 18 x 24" and full size for watercolor paper up to 22 x 30".