An update to the aging M3 vest, M4X armor provides better protection against high-velocity impacts than its predecessor without sacrificing mobility. Instead of a basic vest and infantry 'bucket' helmet, the M4X incorporates full-body protection with armored sleeves, thick gloves, and a full-face helmet complete with a light ballistics-resistant visor.
The armor is also augmented with a lightweight body frame to help the wearer maintain his balance whenever he is hit with tremendous force, like body blows from an onrushing Xenomorph or Yautja. Most notably, and unlike its predecessor, the armor also incorporates light resistance to Xenomorph acid blood.
While the M4X is superior in all aspects to the M3, the armor is still undergoing field testing with several Marine combat units before being issued to the entire US Colonial Marine Corps.