This fits underneath: your light Icebreaker Bodyfit Premium Underwear Siren Tank with wide tank tops. The finest merino corespun with a touch of elastane have significantly improved this undershirt. The body-hugging cut means it fits snugly and is easy to wear with the Siren Bra. The feminine round neckline and arm openings are trimmed with the same fabric. And it also fits over the top: as a t-shirt.