Atom Series: Synthetic insulated mid layers | LT: Lightweight. Lightweight, insulated Coreloft vest, designed to preserve core warmth. Ideal as a layering piece for cold weather activities. This sleeveless core-heater hugs the body with efficient Coreloft insulation to preserve warmth while durable fleece side panels—made with Polartec Power Stretch with Hardface Technology—increase active use breathability and mobility. A wind and moisture resistant outer shell extends stand-alone usability.