A duster.

Lambswool dusters are good and so are the plastic ones that create a static charge.

Are you referring to those thin little fins on baseboard radiators? If so I used pipe cleaners sprayed with Fantastick..it was very tedious just doing the one short rad in the small bathroom but it was caked with fuzz from towels etc. Next I will try shaping and taping a pipe cleaner onto the crevice tool of a vacuum cleaner and doing it that way. If your fins don't look all that bad then I would just suggest blowing the dirt out again with a vacuum cleaner with the hose put on the blower end if yours allows for that.

Thanks bud and pkguy. I actually mean the big cast iron kind. I do have one of the static charged dusters, but there are so many narrow openings at opposing angles in the radiators that it's impossible to reach them all. Is there a duster that's flexible? Mine is not. The blower is a good idea too but my current vacuum doesn't do that.

I have the old cast iron radiators and I finally got a dryer vent brush at Walmart. It is bendy and narrow enough about 1 1/2 in. to fit in all the spaces. HTH Sue

Ah! Sounds perfect, Sue. Thanks!

I use long strips of old tshirts as rags and I manipulate the rags fin by fin through the radiator. Usually spray a bit of vinegar water on the rag first. And for any troublesome spots, I put an old toothbrush to work.