On this BMO model I used 3-core electrical cable which gave me not only flexible arms and legs but also BMO's 3 fingers on each hand! I normalised the fingers with rubber tubing then used heatshrink to give a better working surface. I was happy making little socks out of T-shirt material for the legs but for the arms and hands I wanted something a bit special.
My local hackspace has a good supply of Sugru so I used 2 little packs of blue, 2 little packs of white and just enough yellow (about 40% of a little pack) to get the exact shade of teal I needed.
I used various modelling tools to form the fingers and get a thin, even skin of Sugru over the whole surface and then spent as much time as I could afford smoothing it all out (although I could have carried on for a few more hours I'm sure!)
I promise I'll do a full Instructable once I've finished the software for BMO's face and a couple of "playable" games ("Conversation Parade" and "Adventure Master" - the one with two Abraham Lincolns!)