Catastrophic optical disc shattering blamed on cleaning chemicals and packing foam - another data preservation concern to add to bit rot and laser rot

Bit rot isn't the only worry. CDs and DVDs are also susceptible to damage caused by cleaning or foam off-gassing chemicals.

Shattered CDs and polycarbonate degradation

Discussions about the thorny topic of computer data preservation are swirling again. This time, optical disc collectors are highlighting the danger of catastrophic failures of compact disc (CD) formats. Specifically, a handful of Twitter/X users have seen their treasured CDs split or shatter without any glaringly obvious cause.

The root cause seems to be the degradation of the polycarbonate substrates of the CDs from either cleaning substances or some types of foam padding in storage cases off-gassing. Polycarbonate substrate degradation can occur due to some polyurethane foam padding off-gassing.

The two examples of shattered CDs embedded above might look pretty similar, but the failures may have been precipitated through different vectors.

• @japanretrogame's split-down-the-middle CD was perhaps doomed due to too much care and maintenance. Reader notes suggest the user cleaned and polished this CD to keep it clean and shiny. This eventually caused chemical cracking of the polycarbonate substrate, it is thought [machine translations used].
• @CZ662C's even worse-looking CD fragments: the tech detectives on X reckon this dramatic damage was caused by storage in a foam-padded case. Some foam padding materials will off-gas ammonia compounds. Sealed protective cases with (particularly polyurethane type) foam padding will off-gas, and if left sealed with CDs inside, the vapor can weaken, craze, or lead to cracking of the polycarbonate structure.

Polycarbonate substrate damage is a greater danger for CD users as compact discs rely on a single layer of this plastic. DVDs employ two polycarbonate halves bonded together with adhesive, which makes them less susceptible to the above-outlined issues.

Bit rot and laser rot

There's also bit rot and/or laser rot to worry about. The dangers of bit rot and laser rot have caused far more significant blips on the optical disc user threat radar to date.

Wikipedia classifies this kind of damage as being caused largely by oxidation of the reflective layer, reactions with contaminants, and ultraviolet light damage. DVDs can also suffer from de-bonding of the adhesive between the two slivers of polycarbonate in the disc.

Over the years, some brands of optical media have earned a poor reputation for longevity due to bit rot susceptibility. I've had numerous discs suffer this kind of damage. It is therefore important to back up optical discs, which may themselves have been backups at some point, to keep all your old digital treasures alive.

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Mark Tyson is a news editor at Tom's Hardware. He enjoys covering the full breadth of PC tech; from business and semiconductor design to products approaching the edge of reason.