According to the card, the belt fits tightly to the body and remains barely noticeable under clothes; it can be worn on bare skin or over underwear as needed. Size 48–50 is stated in the name; the material is combed dog hair. The card does not specify the thickness or visibility under particular clothes.
General information (not a manufacturer's instruction): try the belt under ordinary clothes to judge how noticeable it is; hand wash, do not iron – this is also stated on the card.