100% Cotton. Size: 3.8cm length x 3.6cm width / 1.5 x 1.4 inches. Durable plastic bobbins are stronger and waterproof than cardboard, for many years with smooth finish that prevents floss from snagging. Features two thread clips on each board to secure line ends and allows labeling with marker for easy reference. Keeps thread, skein and washi tape organized and untangled.