There is also the Sea to Summit Travelling Light line of Sil-ny bags if you are looking for something extremely lightweight. The downside is that this otherwise strong material is prone to punctures from the corners of crisp packets, candy wrappers and keys. It is a rip-stop weave but still, a bit worrying when it's your sole carry-on. Another downside is that the thin fabric pulls under the weight and it looks really heavy even if it isn't, so expect to be weighed.

Otherwise it worked great for a few of the Thomas Cook flights an ex-client booked us on a few years back. The carry-on limit was 1 bag total max 5.5kg (11-lbs)!