The label says 100% linen, but it's so silky and drapey that it feels like silk and linen. it's not a scratchy linen at all. it's a very very fine knit, but the top is not sheer. i do not think you need a cami under it. 

i bought the xl and the fit is just as shown. it has a slight drape, but it's not really baggy at all. i bought the grey and it looks lighter on-line that it really is. it's a bit darker and has a silver essence also. i liked this so much, i just bought another one in mauve.