Spider Wars, Chapter 1: I Really, Really Hate Clones - S5-E12
Character mistake: When the group of Spider-Men are breaking into the Kingpin's building through the front door, Octo-Spidey uses a laser to cut a circle in the door and then proceeds to tear the door off its hinges with his robotic arms. Since he was just able to simply tear the door off, there was no need for him to cut the hole in the door in the first place. It's not like he needed to reach through the hole with one of the arms to unlock it from the other side.
Answer: There are several substances in canon and non-canon that are resistant to lightsabers. Beskar, also known as Mandalorian iron or Mandalorian steel was used to make armor and weapons by the Mandalorian people. Cortosis was an ore that, when heavily refined, stopped lightsaber blades and blaster bolts. Phrik was another metal, used in Darth Sidious' lightsabers and the electrostaffs used by Grievous' robot guards. Neuranium was a very, very dense and heavy metal that was partially resistant to lightsabers, but was more often used to shield from scanners. The species orbalisk and vonduun crab had carapaces that could withstand the blow of a lightsaber.
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