I'm going to BKS next week for a bespoke jacket. The idea is that it will be comfortable in winter and summer. So the leather will be perforated. It never occurred to me that perforated leather could be suitable for winter. But BKS' police customers have it - they wear a Pertex windproof base layer in winter. https://www.bksleather.co.uk/product...in-windstopper As for warmth, BKS offers linings of Outlast, Polar Fleece or SpaceTec from Heathcoat Fabrics https://www.heathcoat.co.uk/market-sectors/3d-spacer/