RW 主要怕熱，也怕紫外線。相變並沒有比較好，可抹寫比較方便是真的。


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http://www.clir.org/pubs/reports/pub121/sec4.html

4.3 CD-RW, DVD-RW, DVD+RW, DVD-RAM Discs

RW and RAM discs are generally not considered for long-term or archival use, and life expectancy tests are seldom done for this medium. Rewritable discs use a phase-changing metal alloy film for recording data and aluminum for the reflective layer. The alloy film is not as stable as the dye used in R discs because the material normally degrades at a faster rate; however, these discs should still be stable enough to outlast the current CD or DVD technology.

The phase-changing film is affected primarily by heat, but ultraviolet (UV) light may also be a factor in the aging process. The combination of high temperature and UV light may further accelerate the aging process. The combination of high temperatures and high relative humidity will also most likely accelerate the aging process, just as it does with the organic dye used in R discs. No lab test results are yet available on the effects of these environmental conditions on RW or RAM discs.

The data on the phase-changing metal alloy film layer can be erased and rewritten to a limited number of times (about 1,000 times for RW discs and about 100,000 times for RAM discs). This rewriting does, however, affect disc life expectancy; RW or RAM discs archived after the first recording should have a longer life expectancy than those that have undergone several erase-recording cycles. Given the normal degradation rate alone, the life expectancy for RW and RAM discs will be less than that of R discs. Add to that multiple rewrites, and the life expectancy can be even less....
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