Isabel Brown Tank Top

Purchased at an exclusive high end estate sale. There is no size or fabric content label. I selected size small as it measures 17” across. Fabric is soft & a bit stretchy. Unsure what it is ... polyester??? Design label states: Isabel. Measurements: Approximately 17” across from armpit to armpit. Wide bra covering straps. Scoop neck. Approximately 22.5” from shoulder to hem EUC