Vacuum suit

Vacuum Suits are used by both the UNSC and the Covenant for extra-vehicular activity in outer space, intended to protect the wearer from the effects of vacuum and prevent asphyxiation. They also provide protection from dust and other particles which could damage the user and their equipment. Vacuum suits are completely sealed, and come with an extra supply of oxygen, or whatever other gas the user breathes.

UNSC
The UNSC utilizes several types of vacuum suits.

The suits worn by members of the UNSC Marine Corps have a green body suit, with olive-drab armor plates, and a helmet equipped with a HUD and COM systems. These suits were used by Sergeant Johnson and his squad as they neutralized the unsecured data of the UNSC Corvette Circumference in orbit above Reach. They were also used by the teams sent to clear the NAV database of the during the Harvest Campaign in 2531. Bulky, black vacuum suits equipped with self-sealing foam injectors were used by Staff Sergeants Johnson and Byrne during humanity's very first combat encounter with the Covenant.

One type of vacuum suit worn by UNSC personnel appears virtually identical to the universal BDUs worn by the UNSC Army and Marine Corps, but features a fully enclosed helmet and is fully sealed against vacuum. These suits were used by the YSS-1000 Sabre crews who boarded the Covenant corvette Ardent Prayer during Operation: UPPER CUT. Personnel working aboard UNSC refit stations such as Anchor 9 also use vacuum suits.

Black body suit
This body suit is a form-fitting suit of polymer body armor that has systems that mask the infrared signature of the wearer, as well as creating a comfortable environment. The suit is fully sealed, and has an oxygen reserve of 15 minutes. The helmet has encrypted communications gear and a HUD, along with thermal sensors and motion detectors. Unfortunately, the suit's general complexity leads to complications. Over prolonged periods of time the suit will become very uncomfortable to wear, and is difficult to repair in the field.

These suits were used by the SPARTAN-IIs in several missions before they got their MJOLNIR Armor.

SPI Armor
The Semi-Powered Infiltration Armor utilized by the Spartan-IIIs has seven minutes of breathable atmosphere.

MJOLNIR Armor
The MJOLNIR Powered Assault Armor system utilized by the Spartan-IIs has 90 minutes of breathable atmosphere. The vacuum capabilities of the armor were demonstrated during the initial phase of the Battle of Earth, where John-117 utilized the armor effectively in vacuum combat. As well as being completely sealed, the armor can prevent the wearer from burning up in a planet's atmosphere. Later in the Battle of Earth, Spartan-117 fell through the Earth’s atmosphere into the jungle of Kenya, and survived, although he did use a part of the Forerunner Dreadnought as a heat shield.

ODST armor
The most common version of the suit of combat armor worn by the Orbital Drop Shock Troopers is fully vacuum-sealed and includes oxygen reserves for 15 minutes. However, not all of the armor's variants are vacuum-protected, as some variants have leave the neck and fingers exposed.

Covenant
The Covenant also use vacuum suits, such as the blue-and-black suits worn by Kig-Yar Rangers. Sangheili Rangers and other special operations units utilize special vacuum-enabled Combat Harnesses, such as the Assault Harness, Flight Harness, Ascetic Harness and Commando Harness.