Synthetic textiles can shed numerous microfibers during conventional washing, but evaluating environmental consequences as well as source-control strategies requires understanding mass releases. Polyester apparel accounts for a large proportion of the polyester market, and synthetic jackets represent the broadest range in apparel construction, allowing for potential changes in manufacturing as a mitigation measure to reduce microfiber release during laundering. Here, detergent-free washing experiments were conducted and replicated in both front- and top-load conventional home machines for five new and mechanically-aged jackets or sweaters: four from one name-brand clothing manufacturer (three majority polyester fleece, and one nylon shell with non-woven polyester insulation) and one off-brand (100% polyester fleece). Wash water was filtered to recover two size fractions (>333 μm and between 20 and 333 μm); filters were then imaged and microfiber masses were calculated. Across all treatments, the recovered microfiber mass per garment ranged from approximately 0 to 2 grams, or exceeding 0.3% of the unwashed garment mass. Microfiber masses from top-load machines were approximately 7 times those from front-load machines; garments mechanically aged via 24-hour continuous wash had increased mass release under the same wash protocol as new garments. When comparing to published wastewater treatment plant influent characterization and microfiber removal studies, washing synthetic jackets or sweaters as per this study would account for most microfibers entering the environment.