Electrum

Electrum is a golden substance which can be used to render a Transformer virturally invulnerable for short period.

When coated with Electrum, a Transformer turns golden in color and can survive even the strongest of attacks without so much as a scratch.

Beachcomber once found a lagoon full of the stuff, which was promptley seized by the Decepticons.

Sunstorm was also built out of an Electrum Alloy which instantly repaired any damage he suffered. Whether this property is natural of Electrum, or was a side effect from Sunstorm's unusual creation is unknown.