Made out of some heavy duty metal, maybe. XD Also, if you watch some of the animations of his blade retracting or coming back out, it could be a slide mechanism within the blade itself, and then the external part comes together like the early Lancelot swords.
In the end, it is just an anime, right? XD I mean, look at how much is impossible, yet done.
...Radiant Wave Surger, Energy Wings, Knightmare Frames in genereal, and Charles zi Britannia's stamina. Honestly, are we supposed to accept the fact that ONE MAN was able to beget so many kids without flopping over and dying (then again, I suppose that's where Lelouch gets his awesomeness from.)