Material of which it is theorized that the cell in which Professor Phineas Pheasant is being held prisoner by KAOS is constructed.
The glass is impervious to attempts to shatter it using a Silent Machine Gun, a Laser Gun - even a brick.
Tests on a sample made by CONTROL scientists suggest that it will be vulnerable to a high not sung by Madame Rosa La Costa, CONTROL's singing agent, but this, too, fails.
Instead, she simply walks into the cell, her sturdy frame causing the cell to fall apart on contact.
[Episode #113: "Pheasant Under Glass".]