I can only speak from my observations of my own, still young, snakes. I have two yearlings and one '08 (all females) and they are all occupying their own 2x3x1 reptile cage. Each cage is heated with a RHP which is controlled by a Helix. Each cage has climbing/lounging structures as I have noticed that these young ones like to elevate

In less than 6 months the two yearlings will each get their own 6x2x2 AP T20 cage with RHP's. I have decided this based upon thermoregulation needs of the snake. It is my observation that the snakes really use the entire thermal gradient; not just hot or cold. I believe that a snake who is cramped in a space is not able to properly therrmoregulate. Also, I have learned that my boas are far more curious and interactive than my ball pythons. This, for me, suggests that when the snakes choose to interact with their external environment, they ought to have a way to do this and I feel that being in a cage with a glass door allows for this.

For these reasons (thermoregulation and their interactivity) I choose a large cage.

Lots of keepers also keep their snakes in 4 foot long enclosures and this has worked very well for them and for the snake. I just figure that a 6 foot long snake could never fully stretch out and see my snakes stretch out now...well, I think they like to stretch out when they want and I feel that I have a responsibility to provide that space for them!