I need a rope and I thought I'd ask here, my requirements are around 120', dyno, dry, and light as possible. Rope would be used for glacier travel (2 man) and rappels.

Edilrid Flycatcher is lightest (last I knew).

Well let's start with this what thickness should I use? I was looking at the sterling duetto 8.4 but my partner thinks that's too thin.

I've used a 7.7 mm rope for glacier travel and full rappels. Normally I have one about 8mm and 30 m long.

8.4 is plenty, but it's never "wrong" to go a little heavier if it provides one of you with peace of mind. If he's sketched out at the idea of rapping off an 8.4, go to something he's comfy with. Compare the weight differences and see if the peace of mind is worth the extra ounces. He won't have as much fun if he's worrying about the rope the whole time.

Why does he think 8.4 is too thin?

I use a 9.2, but i'm fat...

Yeah I wanted ice floss but he didnt want to use a twin or half rope, I ended up buying a 40m 9.2 fusion nano alpine. 51g per m. It's a lot heavier than the floss but i'll have a rope I can lead climb on after the trip.

^^^^

This is why I have three ropes even though I don't really rock climb.