Dashing Tweeds has the Lumatwill range, which are tweeds with 3m reflective thread woven in with the traditional wool.
While half-metres are £42.50, you can get samples, which are great for small projects. With one of my samples, I’ve made a button corsage, which will be a nice reflective attachment to my bag.
When I get better at sewing, it would be deeply satisfying to make a skirt out of this tweed. Just a flash of light out of the corner of your eye - is it the skirt? Is it something else?