These curtain liners are great for the money.  I definitely feel that they block out a good bit of light (and I'm using them under white curtains) as well as help to keep my bedroom noticeably cooler.  They were a little difficult to hang with my curtains-they kept sliding off of the hooks.  I also wish they were slightly wider, as you can see the outline behind my curtains.  But overall, I am very pleased & would recommend.

Pros: Great value; blocks light; helps to block out heat & keep room cooler
Cons: A little difficult to install; Could be wider so that they show less behind curtains