I like frixion pens but they don't always mark lycra that well I've bought a few different chalk wheel markers over the last few years but not been entirely satisfied by one. The Prym one was dreadful - lumpy uneven line.
In the end, I plumped for a Japanese Chakoner which is very good but also by far the most expensive of the lot. I've used it a couple of times but simply couldn't find it when I needed it yesterday for black cotton lawn. I'm a champion mislayer of sewing stuff at any time, even when it's in plain sight...so, in desperation knowing the chaco pen wouldn't survive the handling, I dashed up to the bathroom and grabbed a sliver of soap that I'd meant to throw away last week
and used that - don't know why I'm so absurdly thrifty with soap particularly but I am. Disposal, not usage I hasten to add!!!
I've known about using soap slivers for marking fabric for some years so why have I never tried it?
I probably thought it wouldn't be easy to wipe off but I was wrong. It takes a bit more brushing than chalk but I couldn't see a residue (yes, even with my reading glasses on) and the quality of line is perfect with a nice thin sliver.
It's the best thing I've ever used. DH uses hand wash a lot but I'm hiding that until I've got a nice stock of slivers.