Simple mirrors
Any flat reflective surface, such as a compact disc, a makeup mirror, aluminum foil, or even a shiny credit card, can be used as a signal mirror. Cases are on record in which items such as these have been used successfully. CDs as reflective devices reflect only about 20 to 25% as much light as a high-quality 3" by 5" plastic signal mirror. The reflective surface needs to be as flat as possible to increase the reflective surface area that is aimed at the potential rescuer. Otherwise, the projected signal may be too weak to be effective. For instance, if using a credit card, use the flattest one you have. Or if using aluminum foil, use the least 'crumpled' piece available and smooth it on a board or other flat surface. Convex- or concave-shaped materials will be less effective than a flat surface.

It takes two hands to use a simple reflective surface as a signal mirror. Hold the mirror close to your eye with one hand, with the reflective side facing away. Stretch out the other hand, and form a V with two fingers. Sighting over the mirror, (or, as in the case of a CD, through the hole), adjust the mirror to aim the sunís reflection through the V of your outstretched fingers and onto the plane, boat, shoreline, or other target. Flash the signal by moving the reflection up and down between the base of the V and the target centered between your fingers.

Better signal mirrors have features to aid in aiming the reflection. Some have sighting holes in the middle, others have aimers that make it possible to use the mirror with one handóessential if you need your other hand on your paddle to steady the kayak. Signal mirrors are available in several sizes and materials. Common sizes are 2" x 3", 3" x 5", and 4" x 5". The larger the mirrorís surface area, the more light it can reflect. For example, a 2" x 3" mirror has a surface area of 6 square inches, versus the 20-square-inch area of a 4" x 5" mirror. The drawback of a 4" x 5" signal mirror is that it is harder to hold and aim with one hand, storage is more difficult, and it may be more fragile. Materials include metal, glass, and plastic. Glass mirrors are the most reflective, followed by plastic, and metal as a distant third. An easy test to perform when comparing signal mirrors at the store is to look at your reflection in the mirror. If your image appears dim, distorted or diffused, look for another mirror.

Metal
Metal signal mirrors are the least desirable, and I donít recommend them. They can require two hands to aim, give a relatively weak reflection, will sink if dropped overboard, and some may corrode quickly. Metal mirrors can reflect as little as 14% of the light received, less if corroded. Even stainless steel models corrode, and lose a substantial degree of reflectivity.