Sewing

I make marine canvas. Sunbrella is a brand of exterior, water shedding fabric. Made of solution dyed acrylic and breathable to a degree. Off the roll it's quite stiff but softens up over time. They also make a line of exterior furniture fabric that has a much nicer hand. It would work for a cloak, not so much for a jacket.

As far as sewability, it depends on your machine and how many layers your design will cause you to sew through. A nice thing about it is it's two sided, there isn't a coating making a right and a wrong side.

I don't have much experience with sewing or machine-compatible fabrics, but have you considered waxing normal cotton? I put a few coats of Sno-Seal on my jacket at the start of every winter and it does a good job of waterproofing and adds another layer of insulation

Depending what you're doing and for how long, many thick materials will keep you dry without being actually waterproof. Most of them will require deliberate drying if they're fully soaked, and of course an outer layer with the capacity to shed some water will multiply the time the inner layer can keep you dry for.

For regular walking around, it's worth trying some cloak materials you're using anyways to see how well they handle water.

When I google "waterproof fabric," there are a lot of canvas materials and some polyester ones that come up. Waterproof canvas would be good, but good have to make sure the machine can handle heavy materials - some can, some can't.

There are lots of options, though I can't say which is objectively the best. There's usually a trade-off between waterproofness and breathability. For a cloak you probably also want something with a bit of thickness and weight so it drapes nicely.

I would start by looking at soft shell fabrics with a DWR treatment. Seattle Fabrics sells sample packs so you can feel them before you buy a lot.

Tents and rain jackets typically use nylon or polyester fabric coated with silicon, polyurethane, Teflon, or some other waterproof material on the inside face, and a DWR treatment on the outside face. I expect a cloak made with these fabrics will be too light and crinkly to hang nicely when worn. The fabrics also tend to be slippery so you might tear your hair out trying to keep your seams straight.

You can get great waterproof performance with PVC-coated nylon. Though it will feel like you're wearing a duffel bag.

Waxed/oiled cotton looks awesome but I have never liked the feel. It's also mediocre as far as waterproofness goes.

@[email protected] @[email protected] @Shkshkshk I made a full-circle cloak of 24-ounce-per-yard navy blue wool that I washed and dried before cutting. It sheds rain and snow quite well. After about a decade of regular use in all conditions and locations, it’s still going strong. The cost, of course, is the weight, but the wearer loves it. It’s not about the right product; it’s about the right product for you.

If cost isn't a problem there's ventile/etaproof. 100% cotton and can withstand rain for 2 hours. Add a second inner layer and it's even longer