I do a lot of night ridding. Mostly way out in the country. I've got some really bright lights on my bike, but I have had times when the battery in my taillight runs low and farmers would pull up beside me to tell me that they could barely see my light or me. And with the light being behind me, obviously it's hard to tell if the batteries are running low. So I've bought some SOLAS retro-reflective tape and put it on the rear fender on the Motobecane. I chose SOLAS because it's USCG approved (for watercraft and life vests) and figured that it would be good and waterproof. Also, if it's bright enough to see someone bobbing about in the ocean at night, surely it's bright enough to see a bicycle on a street.
So here's how it looks on the fender under the kitchen lights:
It blends in quite nicely with the fender! I cut three strips. A wider strip to go down the center between the two black lines, and two narrower strips for each side.
Here's how it looks with the lights off using the flash on the camera:
That's pretty bright! It reflects a lot more than the piece of reflective ribbon I've got tied on my bag. Now to take it out for a test run. See if I can get some pictures with car headlights shining on it.