Small Arms Protective Insert The Small Arms Protective Insert ( SAPI ) is a ceramic trauma plate used by the United States Armed Forces . It was first used in the Interceptor body armor , a ballistic vest . It is now also used in the Improved Outer Tactical Vest as well as the Modular Tactical Vest , in addition to commercially available " plate carriers " . The kevlar Interceptor vest itself is designed to stop projectiles up to and including 9x19mm Parabellum submachine gun rounds , in addition to fragmentation . To protect against higher velocity rifle rounds , SAPI plates are needed . ESAPI . In May 2005 , the U . S . Armed Forces began replacing the standard Small Arms Protective Insert plates with the Enhanced Small Arms Protective Insert ( ESAPI ) . An ESAPI provides protection from . 30 - 06 M2 Armor - piercing rounds with a steel or tungsten penetrator , but costs about $ 600 per plate , 50 % more than SAPI plates . They are produced by Ceradyne , BAE Systems , and ArmorWorks Enterprises . XSAPI . A call for a next generation plate , to stop even greater velocity threats than the ESAPI plate has been issued by the U . S . Army . They have specifically allowed scalar or flexible systems , and are also calling for greater coverage , with less than a pound of additional weight . Materials and capabilities . The standard plate for the Interceptor body armor is made of boron carbide or silicon carbide ceramic . New ESAPI plates are also made of boron carbide . The standard plates are not given an NIJ rating , as they are tested in accordance with specific protocols for the military and not the NIJ ' s testing . Military testing calls for survivability of three hits from the round marked on the plate - for standard SAPI , of a caliber up to 7 . 62x51mm NATO M80 ball and of a muzzle velocity up to 2 , 750 ft / s ( 840 m / s ) . For ESAPI , a . 30cal M2 AP ( . 30 - 06 black - tip armor - piercing ) cartridge . This performance is only assured when backed by the soft armor of the OTV ( or any soft armor which meets military requirements for protection . The ceramic plate is backed with a shield made of Spectra , a material up to 40 % stronger than Kevlar . , to trap any fragments of either plate or projectile and prevent them from injuring the wearer . Sizes and weights . SAPI plates meant for body armor come in front and back plates which are identical , and smaller side plates . The front and back plates come in five sizes . Their dimensions are the following : Front and back SAPI plates : ESAPI plates are the same size but slightly greater in weight . Torso side plates are as follows : Physics . The mechanism of effect lies in absorbing and dissipating the projectile ' s kinetic energy in local shattering of the ceramic plate and blunting the bullet material on the hard ceramic . The Spectra backing then spreads the energy of the impact to a larger area and stops the fragments , reducing the likelihood of fatal injury to the wearer . " It is a false assumption that eliminating the penetration of a projectile into the body by using a personal armour system absolves the wearer from serious injury or death . " The same principle is used for the ceramic tiles used for the armored cockpits of some military airplanes , and the anti - spallation liners used in modern armored personnel carriers .