This tank fits very flattering with a seamless fit, much like seamless microfiber underwear. The spandex gives it a glittery shine when you stretch the fabric, so it can be casual, but can also go underneath a nice shrug or dressy jacket.
The underarm holes come all the way up, so it has support and doesn't show bras, etc.
However, the material is much thinner than they are specifying. I love the feel of the material. I will be wearing it underneatch a shrug/cardigan, but if you wear it by itself it will be a little sheer.