http://www.body-con.co.uk/
look here....
They appear to be stretchy stuff. As a large lady myself, I cannot think that they would be flattering, but I guess it depends on your build - they wouldn't do anything at all for me!!
I am also a larger lady - body con I would say is for very thin ladies, it will show every lump and bump =) Although if you are confident and have a nice figure then go for it!!!!
I thought they were strectchy but clingy dresses that as has been said show every curve. V Beckham is a fan and to be honest don't think they look nice even on a stick like her.