John,

Polar Bear guard hair does in fact have a hollow core, although I'm not sure how its buoyancy relates to other hollow hairs, but something tells me it is less buoyant since I've only seen subsurface flies using it.

It is also colorless. It was once thought to have fibre optic qualities, but it's since been proven to be light 'scattering/reflecting' (the walls of the core are rough) rather than light 'conducting'. Similar to how snow appears white, although it's made of water.

BTW, one of my favorite flies is the Black Ghost tied with a polar bear wing.

------------------
CD
-----------
Chris Del Plato
Long Valley, NJ