Transparency means a brand publishes the names and locations of its Tier 1 (final assembly) factories at minimum, and ideally Tier 2 (fabric mills, finishing) and Tier 3 (raw materials).
The Fashion Transparency Index ranks 250+ brands annually on disclosure quality. Open-supply-chain registries include Open Apparel Registry and the Walk Free Foundation's modern slavery index. Look for an annually updated factory list with addresses, worker counts and audit dates.