Kobuk - your links go to real feathers dyed fake colors.
NOT a good idea for a fursuit! Real feathers aren't always durable, and are prone to attracting mites. Long-lasting real feather costumes have to be periodically stored in the freezer or sprayed with chemicals to kill the mites.
I make feathers from all sorts of things, it depends on the size, shape, color, and style I'm after! Foam is probably my number one go-to for feathers, craft foam is really good for them, though you have to treat it gently. For more durable feathers I've often used fur, and I've used plain old cotton fabric as well.
That tutorial is pretty neat, I may try that out one of these days. Though it's time-consuming as heck, looks like.