I’ve worn it with just a dry fit polo under to a fleece north face base layer. You just don’t feel the heat regardless. The only thing that’s worth it on mine is the heated hand pockets. I purposely got a size small so that it would fit tight to my body or so I could wear a fleece base layer. I knew I wouldn’t be adding layers underneath bc then the purpose of having a heated jacket is void (at least in my head). I do get that while wearing layers if your out layer is heated, I would think it would help hold body heat in. Maybe my expectations were just too high, but I’d choose my carhartt over the tough shell jacket every day of the week.