Depending on your personal needs and acceptance level the see through or sheer intensity or lack of is a completely personal and individual choice.
Win this bikini for you and your friend, see previous post! One Piece Thong Bikini in Mind Visions Rainbow.
The transparency level is measured using a unit of measure called a denier, from 3 extremely thin, barely visible to 15 standard sheer for stockings up to 30 semi opaque until 100 opaque.