It depends on what you are going to use the liner for. If you are using it to add warmth then there are other options to a liner. If you are using it keep sweat, dirt and so forth off of your bag then I would recommend something light like a silk one made by Jagbags.

In warmer weather I use a silk Jagbags liner. It is a mummy shape and weighs right at 5 oz. If I am going to be in colder weather where I can wear my clothing inside my bag then I don't use the liner.