You should look at photos. Most prisons don't have single cells, they have large rooms with bunks, or they have shared cells with 2 or more people in each one.

They should make cells that are tiny and fit one person - but have lots of opening and permission to talk to anyone around them.

That way there is physical isolation, but not mental isolation.

>They should make cells that are tiny and fit one person - but have lots of opening and permission to talk to anyone around them.

Actually there's no need for the cells to be tiny -- even if they are meant for just one person.

That's not entirely true. If the cell was large people would attempt to get into them on purpose to get a private room.

The cell has to be small enough that no one would prefer it over general.

Additionally if the cell was larger then the number of neighbors each prisoner could interact with is reduced. But the goal is to give them the opportunity to interact with as many people as possible.

> If the cell was large people would attempt to get into them on purpose to get a private room.

I think that's a societal problem, not a prison design problem.

> The cell has to be small enough that no one would prefer it over general.

Why? Wouldn't it be sufficient discouragement just with the removal of your basic rights to go where you like and do what you want?