If you want to be visible to cars at night, use their headlights in your favor! Retroreflective tape can come in all colors -- even black -- but it will glow a bright white in a car's headlights.

I bike quite often when it's dark out, so I added big strips of this tape to my messenger bag. Hopefully, this means that I will be run over by cars less often.

In this instructable, I wrote a little background on how retroreflective tape works and then I show how I attached it to my bag, using contact cement.

Thanks to Oscar, who helped out and took a lot of these photos.

## Step 1: About Retroreflective Tape

So, what is retroreflection? Basically, it's the property of some materials to reflect light right back along the same path that it first hits the material. Note that this is different from a a mirror, which will reflect light off at a different angle.

If you have a light shining at a retroreflective material, any light that hits the material will reflect directly back at the source of the light. The result is that if your vantage point is close to that light, the light will be bouncing right back at you, which means that it will appear really bright to you.

There are a number of before/after photos in this instructable. On the left side, you see what retroreflective tape looks like in the daytime (i.e. when light is fairly diffuse and not localized to the camera's vantage point.) On the right side, you see what retroreflective tape looks like at night (i.e. when it's dark out and most of the light is coming from the vantage point of the viewer.) I simulated this by using the flash on my camera, which is right above the lens.

Retroreflection can be achieved in a number of ways. On a large scale, a set of three orthogonal mirrors (like the corner of a cube) will do the trick: no matter where you are, your reflection will appear in the exact middle of that corner. This principle can be applied on the small scale (as a continuous surface, like on tape) as a fine-grained texture. Retroreflection can also occur in transparent spheres; for certain materials, light entering in any direction will be focused on the edge of the sphere on the opposite side, and if that can be made reflective, then it will come shooting out in exactly the right direction.

The last type of retroreflection is how the tape works that you see in this instructable. It's a black surface, but with millions of tiny beads embedded in it. Each one will retroreflect, resulting in a whole, retroreflecting surface.

I've tried to explain retroreflection simply, which leaves out a lot of precision. If you'd like to learn more, here are some resources:

## Step 2: Materials

To do this project, I used:

• Messenger Bag: My beat-up Chrome bag (oh, how I love it so.)
• Contact cement: This is an industrial-strength adhesive. It's strong and flexible, though a bit smelly for a few days until it finishes curing.
• Retroreflective Strips: I got a bunch off ebay. The amount you see here was about half of the stuff out of a \$15 batch.
• Drawing and Cutting Stuff: A ruler, pencil, and a sharp utility knife for cutting the retroreflective strips.

## Step 3: Clean and Prep

Gotta take off that old Instructables patch. Also, since I want the reflective cloth to lie flat, I removed the Chrome logo from the flap. I just used a utility knife to carefully cut the stitching, peeled off the patch, and rubbed the old adhesive off.

## Step 4: Cut Out Retroreflective Fabric

Next, I laid the retroreflective strip over the area I wanted to cover and penciled in the outline of the shape I wanted to cut out, using a pencil. I inset this a little bit to leave room around the edges, then cut it out with a utility knife. Finally, I laid down the cut-out shape to make sure it fit right.

## Step 5: Contact Cement It On!

Contact cement is not totally straightforward to work with, so read this step carefully if you haven't used it before.

First of all, work in a well-ventilated area. The fumes from the glue can be bad for you.

Now, contact cement works best when it is applied to both surfaces being joined, and then allowed to dry a substantial amount before the surfaces are pushed together. I started with one end of my large strip, applying contact cement to a similarly-sized patch both on my retroreflective strip and on my bag.

Then, I waited about twenty minutes for the cement to dry. It should be barely tacky before you join it together. I lined up the pieces and pressed very firmly for a few minutes to get good adhesion. I later put a piece of cardboard on top and actually stood on it, which worked well.

Once the first patch was connected, I applied cement to both surfaces for the rest of the strip and the bag, and repeated the process.

## Step 6: Finishing Touches

Finally, Oscar put on a few more strips on the strap of of the messenger bag, which makes me visible from the front, too.

And that was it. Presto! No more getting run over by cars at night. Hopefully...

As a finishing touch, I glued on one of our new Instructables Robot patches. Now every car that's about to run me over can also get a little dose of the Instructables brand.
I think you've got the wikipedia (You mispelt it as well) and the manufactorer's explanation links mixed up.
Thanks! Fixed.
great job, but some notes on locating your material would be good. i.e. place it where drivers will see it. hit just below your seat post release, put a stripe on your handlebars. i'm -very- happy to share the road, and make certain to give cyclists plenty of room, which i've seen is not common, however, a significant portion of cyclists ride with no lights, no reflective material, and completely ignore traffic signals. all the reflective gear in the world won't help much when you run a red. noodle you can get material by length, although you'll probably find things more conducive to belts that shirts. hit up a surplus place (like axman surplus in minneapolis) and you'll be able to but rolls of it. an automobile parts store will have some in sticker form for trucks that would work for belts. for clothing you'll probably need to contact a specialty fabric store, it is available as fabric paint( think road worker t-shirts) but i'm not too clear on it's non-industrial ease of use.
The non-sticky, sew or glue-on kind is easy to get at normal chain fabric stores. Sometimes you can find it in big box chain stores like Wal****, in the bike sections.
I wrapped this in a spiral around my front and back forks (think like candy cane stripes). I didn't need to glue, just one piece of duct tape at the top and one at the bottom to hold it in place. It reflects from almost any direction. I like it because I won't have a lot tape residue when I want to take it off. One bike is silver so it doesn't show, the other is red but the junkier it looks, the less likely it is to get stolen.
Dang it!<br/><br/>At first I was going to say, &quot;stick an Instructables patch on it, then that'll be awesome.&quot; Then, I realized there <em>was</em> one.<br/><br/>So I was going to say, &quot;stick an Instructables Robot one, that would be even better!&quot;<br/><br/>Unfortunately, you didn't let me say that, and you beat me, making my body burn into a pile of ashes.<br/><br/>+1 rating.<br/>
Can you get retroreflective material by the metre? Cause I'd love to have a shirt entirely made out of that. Maybe a belt would have to do... Anyway +1, great instructable, good photos!