Ive always used foam pipe insulation. Its really, really cheap, and available in a variety of inner diameters for those of us who deign to own OT bikes with bloated headtubes/steerers. ½ piece at the bottom and a chunk long enough to catch the steerer threads on the top and provide a little friction. If youre nervous, you could always hold the stuff in place with a zip tie.
Two bucks will buy you enough insulation to do about 20 bikes, and theres no lingering odor
Cheers,
Derek Vandeberg
Bigfork, Montana