I would highly recommend you read Doug's pages on signal mirrors. Here is a quote:
NOTE: We are often asked about, or see the recommendation online and elsewhere, the use of a CD-ROM as signal mirror. It is shinny, reflects light, has a hole in the center, and thus looks somewhat like a signal mirror. Moreover, many of us have lots of useless CDs around, AOL continues to send many of more of them, thus its appeal.
In tests a CD proved to be only about 20%-25% as effective (distance and brightness at distance, judged subjectively) as a 3 x 5 mil-spec plastic signal mirror, a bit more effective, but not even 50% compared to a small 2 x 3 mil-spec plastic signal mirror. It would compare worse against higher quality mirrors.
From an operational persepctive, in an After-Action Report of a major SAREX (Search and Rescue Training Exercise) conducted in 2001 by the Colorado Wing of the Civil Air Patrol, the conclusions were, "that "victims" who had never used a signal mirror (with the aiming hole in the middle) were able to use them effectively, while CD's (AOL etc.) are useless as signal mirrors." CD's come up often in the forum as their price is right and if it was all I had....blah blah...however a quality signal mirror is vastly more useful and efficient. If you are building a kit I would recommend you do not scrimp on this item.
See Doug's write up here:
http://www.equipped.org/signal.htm#ReflectionsOfLight I have both Malcolm Murray's Rescue Reflectors and others including the one in Doug's kit.
I tested my 2x3 Rescue Reflector plastic model at Crater Lake Oregon last year. I was about a mile or so from my wife who was at the lodge. I contacted her via ham radio but she could not see me. I took out my mirror and brought the fireball right down to where I knew she was standing and she immediately yelped into the radio that it was nearly laser blinding.
A decent quality signal mirror is just not so expensive to be substituting a free inadequate CD.