In my experience, I'd rather have a liner that's very thin, with zero insulation. but made of windblocking nylon. That way I can get it as close to my body as possible and have the largest amount of flexibility of insulation between the liner and the outside jacket. If it's just cool then I ride with the liner and the outer jacket. Cold then it's the liner, a fleece jacket and then the outer jacket Freezing, then it's the liner and a down jacket and the outer jacket. If the liner was insulated, it would: A. cost more B. not work as well in a wide range of temps C. be bulky and less comfortable to wear.