From Halopedia, the Halo wiki
The helmet is comprised of components similar to those used by Marines, and the helmet has a "Team endurance catalyst" intel suite. In addition, the Soldier helmet is also noted for its low power consumption and is one of the most comfortable MJOLNIR helmets to wear due to the excessive attention paid to ergonomics in its design.
The legs have a shield emitter junction, heavy plated boots, and fixed soft cases. The armor has a variable case structure, which extends combat as operators will have more equipment, ammo, and materials. All these cases have minimal disruption on most Spartan-IVs. The armor also has both fixed and modular composite layers, and additional magnetic hard points.
Having entered service by January 2553, the Soldier-class variant was manufactured by the Materials Group and tested at the Damascus Testing Facility on Chi Ceti IV. Soldier-class armor functions in a support capacity on the battlefield as operators equipped with this armor can carry substantially more equipment than Spartans wearing other armor types, while retaining their field mobility and dexterity.
The GEN3 iteration of the SOLDIER helmet features a new revision of Materials Group's combat catalyst firmware. The fireteam synchronization features remained unfinished, but Dr. Halsey's interest may accelerate development.
Halo 3 MCC - Prototype
In the Halo: The Master Chief Collection version of Halo 3, the Soldier variant was added as part of Season 5: Anvil content. With the updated Halo 3 armor customization options, the players can now fit their Spartan with Soldier helmet, chest, shoulders, forearms and legs. The description of the armor pieces are the same for every set.
Halo 4 - GEN2
Halo 5: Guardians - GEN2
The Soldier returns in Halo 5: Guardians. The helmet and body armor are unlockable as armor permutations through the Requisition system. The body armor includes the Soldier chest and shoulders, unknown forearms, and unknown legs. The Soldier set has three alternate skins: Dogface, Leatherneck, and Rebel.
Halo Infinite - GEN3
The following attachments are not exclusive to Soldier, and are compatible with other helmets on the Mark VII core.
Halo 5: Guardians skins
List of appearances