Best Men's Jacket for Ireland in September?

Michael, I have two, and prefer one. That is the Tilley. It is very expensive but well made, in Canada, and fully functional. The other has pockets for everything under the sun, is not well made and is made on the other side of the world. You might think about a light rain jacket over a sweater. I have two from Eddie Bauer, one a jacket, the other a coat. Both are in the WeatherEdge line. I take the coat to Scotland because you never know when the raindrops will fall. The light jacket goes everyplace else we travel to. I look at my travel clothes as an investment so the cost of the Tilley jacket was easily justified. It will shed some rain but is not waterproof. The Tilley jacket has a zipper front, snaps on the cuffs, and enough pockets to carry what you need without being ridiculous. I like the Eddie Bauer coat and jacket because the hood zips off. All of these will fit in a medium size compression bag.

I like a gore tex rain jacket and a fleece. It seems to rain a lot in Ireland. Not very hard, but often.

My Husband likes Columbia brand jackets and fleece.

Yes, my buddy who spent a whole year there said that a Gore-tex type jacket and a local sweater - Aran Jumper - real Irish wool, but not too heavy, is THE combo to go with. Here in Colorado we're always about layering, and it looks like the best strategy anywhere. Grins.

Last trip I went with a rain shell and a soft shell. The rain shell will be needed whenever you run into rain - which is likely in Ireland any time of year. I used to pack a polar fleece as a warmth layer but decided a soft shell is more presentable as a jacket on it's own without the shell. It's also water and wind resistant, which can be helpful. Leather looks nice but is heavy and can be ruined by rain. If you want to go that route, there are polypropolene versions that look like leather and don't cost much. I'm surprised how much they look like the real thing.