Since the date on the bluray date comes really close to the plastic protective part [then DVDs] they put a scratch resistance layer on it, so they are hard to scratch but they aren't scratch proof.
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Hard-coating technology
Since the Blu-ray Disc data layer is closer to the surface of the disc compared to the DVD standard, it was at first more vulnerable to scratches.[52] The first discs were housed in cartridges for protection, resembling Professional Discs introduced by Sony in 2003.
Using a cartridge would increase price of already expensive media, so hard-coating of the pickup surface was chosen instead. TDK was the first company to develop a working scratch-protection coating for Blu-ray Discs. It was named Durabis. In addition, both Sony and Panasonic's replication methods include proprietary hard-coat technologies. Sony's rewritable media are spin-coated, using a scratch-resistant and antistatic coating. Verbatim's recordable and rewritable Blu-ray Discs use their own proprietary hard-coat technology, called ScratchGuard.
All Blu-Ray Disc media is required to use hard-coating. DVD media is not required to be scratch-resistant, but since development of the technology some companies like Verbatim implemented hard-coating for more expensive lineups of recordable DVDs.
Blu-ray Disc - Wikipedia, the free encyclopedia