The light version of Mammut's classic performance fleece, the Aconcagua Light ML Jacket has the versatility to work for a whole range of outdoor activities. The Polartec Powe Grip fleece hangs on to our body heat for lightweight insulation while also wicking moisture and breathing if things get steamy. It's also synthetic, so it insulates when wet and also dries quickly—making it more low-maintenance than down. The Aconcagua's warmth-to-weight ratio makes it a nice outer layer for mild weather, and its close-to-body fit layers easily under a shell for a shoulder season mid-layer, too.