The Helly Hansen H2 Flow is a lightweight outdoor fleece which offers a revolutionary take on ventilation teamed with traditional fleece insulation. The core of the jacket is constructed with a synthetic Polartec midlayer brushed fleece, with air pocket perforations with a polyester shell outer fabric that locks heat inside the air pockets for trapping heat & insulating effectively without adding bulk. Key ventilation is offered in the form of zippers in the front which allows for mechanical ventilation & stimulation of air flow, enhanced by an open mesh internal construction which allows for air to flow between the air pockets & the body during intense activities.