Thermite paste

Thermite paste is a chemical used by the UNSC for stealth missions where soldiers may encounter steel doors or other obstacles. It is an alternative method to blasting for neutralizing such obstacles. Plasma cutting can also work, but takes more time.

The paste is likely comprised of iron oxide, used specifically to "burn" aluminum metal to make aluminum oxide, as in a typical Thermite Reaction. It is applied to the surface of the obstacle and then lit. Once the paste is ignited, it produces a huge amount of heat and light, and when fuel is exhausted, a hole should be melted through the obtacle making it very easy to reach the other side.

The SPARTAN-IIs have used thermite paste occasionally to infiltrate human structures, most notably during the Battle of Sigma Octanus IV.