This set of high-quality, durable plastic containers helps to illustrate and reinforce concepts of volume, mass and capacity, and how those can relate to different shapes. The set includes six containers of different shapes: two rectangular; two cylindrical; and two triangular. Each container is 11 cm (about 4") high, but of differing widths and depths so that they hold either 250 ml, 500 ml or 1 litre (1000 ml). Each has markings for either every 50 ml or every 100 ml. Transferring liquids or other pourable materials like sand or beads from one container to another illustrates that different shaped containers can actually hold the same amounts. The containers are heavy-duty and washable for years of use (we recommend hand-washing).