I dyed some Worsted weight, Superwash Merino yarn in a semi-solid neon pink called Scrunchie which is a very bright "need your sunglasses" fluorescent pink. This colour will fluoresce under black light.
100% Superwash Merino
Worsted Weight, 4-ply
For best results I recommend handwash cool, dry flat.
The cost is for one skein though multiples may be available - please select your quantity from the drop-down menu.