Shield + is the most breathable waterproof Pertex fabric. While not as breathable as eVent or Gore-Tex Active Shell I’ve found it pretty good. As well as quite breathable the Rab Xiom (how do you ask for that in a shop?) overtrousers are well-designed and comfortable. The long zips mean you can vent them if you start getting sweaty inside and easily pull them on over any footwear. They’re not long enough for access to inner trouser pockets though. The stiff inner flaps should repel any rain that gets through the water-resistant zips.
The Xioms are light weight and pack up small for carrying. The cut is reasonably roomy without being baggy. The articulated knees allow freedom of movement. The nylon fabric does rustle a bit but not as noisily as some. My only real complaint is the lack of choice in leg lengths – especially as the one length available is too long for me. If the leg length is okay there’s nothing really wrong with these overtrousers though.