These aren't exactly waterproof, as Kuretake Clean Colour brush pens (water based ink) will smear them. Zebra Midliners will also smear them. Fude Touch Sign brush pens play nicely with them however.
Despite that, these pens are great. Crisp black ink, smooth to write, and you can get a couple different line thicknesses with a single tip size depending on how the pen is held.
