What's the thickest, most insulating, warmest base layer on the market? With a high neck? When commuting by bike through the winter, I try to get away with two upper-body layers, to minimise space needed for trying to get stuff dry at work. This is ok down to about 3 degrees, as my current thickest base layer combined with warmest jacket are pretty good. The base layer is Assos's warmest one from about 10-12 years ago - it's good, but not actually all that thick, and there must be warmer ones on the market. So, interested to hear recommendations for thick high-neck warmest-you-can-get base layers....... Anyone tried Rapha's hooded Deep Winter Base Layer? Or their Winter Base Layer?