Just suppose you were to consider this question 40 years ago. Here in the Netherlands, you could pick up this issue of Marion.
It had all the new trends: little tops, like the one on the cover,
some dresses with clean lines, which came with the recommendation to make them in white. Seriously, does anyone recall a summer when white was not an 'in' colour?
The month's trend item was a choice of midriff-baring trouser-and-tank-top sets, made in stretchy crushed velvet.
There was also summery eveningwear,
and tunic suits were hip for day and night.
And of course, the children weren't forgotten either. After all, what would 70's Marion be without some scary drawings of kids?
In all this, it seems like the fabric of choice was printed polyesther-cotton blend. This scares me a bit. Have you ever felt 70's polyesther blends in a vintage store on in your mother's or your own shelf of 'clothes which time forgot'? That stuff is so plastic-y, I can't imagine one would enjoy wearing that in summer...