Originally Posted by MichaelW

All natural fibres come in different grades or diameters. Fine grades are suitable for use next to the skin. Coarser grades are itchy, so better suited to midlayer use.
Fine grades of merino (superfine grade) is a very expensive product, so is often diluted with coarse grades or with synthetic fibres.
With any baselayer, use a suitably breathable shell and insulating midlayers to control heat loss. If you are sweating heavily every day, wear less insulation, and less windproofing. Save waterproofs for actual rain.
On a winter commute there should be no need to sweat.