When the temperature drops, our ultra-lightweight thermal long johns add a cosy extra layer. Regular fit, with supersoft seams, heatsealed care labels and moisture-wicking fabric for maximum comfort. Our clever Heatgen™ technology uses an innovative fibre blend, helping your body to generate and retain heat so you can stay warm when the weather gets chilly. Fly front fastening. We only ever use responsibly sourced cotton for our clothes.