A4 size, thick to accommodate ants of very large size, individual cells that hold very well if you flip the nest and easy for a small cleaning, the partitions very practical to start with a small colony, the moisturizing system very well thought out is sliding drawer... I have several nests but this one is by far the one I prefer! He comes up, so no missing room. By cons, it took me the day to disassemble it, remove the protective paper, wash it (it released a strong smell of chemical that disappeared when washing) and reassemble it. Just a flat: a screw was twisted and cracked a piece of the plexi. But he's worth his price... My dad will offer me the second;-)