The ark was made of the papyrus which was commonly used by the Egyptians for light and swift boats. The species is no longer found in the Nile below Nubia. It is a strong rush, like the bamboo, about the thickness of a finger, three cornered, and attains the height of 10 to 15 feet. It is represented with great accuracy on the most ancient monuments of Egypt.
Slime and pitch - The “slime” is probably the mud, of which bricks were usually made in Egypt, and which in this case was used to bind the stalks of the papyrus into a compact mass, and perhaps also to make the surface smooth for the infant. The pitch or bitumen, commonly used in Egypt, made the small vessel water-tight.
In the flags - This is another species of the papyrus, called tuff, or sufi (an exact equivalent of the Hebrew סוּף sûph), which was less in size and height than the rush of which the ark was made.