The last decade has seen a considerable increase of online shops for fashion goods. Technological advancements, improvements in logistics, and changes in buyer behavior have led to a dissemination of apparel goods and respective data on the Web. In numerous domains of knowledge management, ontologies have proven to be very useful for sharing meaning among organizations and individuals, and for inferencing. With schema.org, there already exists a collection of widely accepted Web vocabularies for the fields of gastronomy, accommodation, entertainment, sports, or products. Yet, schema.org still lacks a dedicated fashion ontology, which would allow for greater interoperability, higher visibility, and better comparison of fashion products on the Web. In this paper, we design and evaluate a Web ontology for garments as a compatible extension of schema.org. For our proposal, we take into account current best practices of Web ontology engineering, we formally evaluate our conceptual model, and we present practical use cases. We further contextualize our work by comparing our approach with state-of-the-art vocabularies for the fashion industry.