Scotchlite is
3M's
brand name of that
cool material that reflects lots (I mean
lots, it's
retroreflective) of
light when
light is shone upon it. It's commonly used as
safety striping, and for letters and numerals that need to be visible at
night. Scotchlite is a
patented material, and may be bought wholesale in
rolls from
3M, or built into
retail products such as
safety vests,
phat pants, etc.
The near-magical reflectivity is due to its specialized manufacture. Special fabric is first made that is woven as a network of interlocking octagons and squares, like so:
__ __
/ \__/ \__/
| |__| |__|
\__/ \__/ \
|__| |__| |
/ \__/ \__/
| |__| |__|
\__/ \__/ \
Adhesive is applied to this material, and while it is still tacky, hollow glass microspheres are cascaded down the material's surface. They are about 50 micrometers in diameter, and are just the right size to fit into the octagons in the material, where the adhesive holds them in place. The microspheres are not colored or coated, but reflect light due to the relatively high albedo of plain glass. The surface of the material is "sanded," leaving hemispheres, which are what allow the light to return to it's source in a straight line.
Not all retroreflective material is Scotchlite. The material used as a backing for stop signs is not fabric at all, but instead microspheres adhered to a white paper that can be printed on with translucent inks. The microspheres may or may not be coated with aluminum for added reflectivity. There are usually between 500 and 2000 microspheres per centimeter of these kinds of material, and it uses whole spheres for reflectivity, making the reflected light visible in all directions, and making it not truly retroreflective.
Scotchlite colored by gluing a transparent layer of the appropriate colored plastic over it. The plastic is itself glossily reflective, and colored Scotchlite looks crystalline, beautiful, and wonderfully futuristic. It comes in the colors White, Gold, Yellow, Lemon Yellow, Orange, Red, Ruby Red, Light Blue, Blue, Green, and (I don't quite understand this one), Black.
Pricing for (colored or uncolored) Scotchlite, as of April 2001, is $220 for 10 yards of 24 inch wide material, or $3.67 per square foot. In comparison, denim from Wal-Mart costs about $.44 per square foot. Scotchlite is not cheap, which is the only reason I have not yet made a pair of pants entirely out of it :-)