Card thickness for formers

A little help needed here, I have done 5 or 6 models all were made with paper outer skins (no formers). I want to make an aircraft model that includes fuse and wing formers.
I am a little unsure as to what card thickness to use for the formers. I know that they are usually thicker than the skin card. At the moment I have some 200gsm card would this be suitable or would I need something thicker?

Thanks in advance