All of the animals in this stack are made from a single 260E balloon. The 260 means that it is 2 inches in diameter, and 60 inches long when inflated. 260A balloons are Average strenth walls, and are easier to inflate than the 260E, which are Extra strength walls.
Some manufactures make balloons out of plastic, while others are pure latex rubber. I am told by the magic store owner where I get my balloons that professionals prefer the rubber balloons because they are less squeeky.
There are also other balloon lengths and types, such as body balloons, which are often multi-colored.