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 and insulating effectively without adding bulk. Key ventilation is offered in the form of zippers in the front which allows for mechanical ventilation and stimulation of air flow, enhanced by an open mesh internal construction which allows for air to flow between the air pockets and the body during intense activities.