Not all silk jersey is the same. We use a heavier weight jersey for our thermal wear, so our garments will keep you warmer and last longer. We don't mix silk with other fibres as we believe that pure silk gives the best thermal performance, (and also that it is the softest against your skin). We make these garments in the UK.
Silk jersey has superb thermal properties, yet its low bulk means that you can wear it discretely under your everyday clothes.