A sleeping bag with down-synthetic filling is often designed to achieve a more favourable price. It can mean that down is mixed with polyester flakes,...
A sleeping bag with down-synthetic filling is often designed to achieve a more favourable price. It can mean that down is mixed with polyester flakes, but also that, for example, the underside is fully synthetic-filled. The compressibility of down-synthetic flakes is good, of polyester layers less so. An underside with polyester filling can be positive for the temperature range because it loses less heat when you lie on it.