From Halopedia, the Halo wiki
When activated, the Drop Shield generates a blue-tinted spherical protective energy shield, and also provides a regenerative effect to those within it. The regeneration is a side effect not fully understood by the UNSC, and was still under investigation by 2552.
Unlike the Bubble Shield, the Drop Shield will expire if it takes too much damage. The shield is enabled by a small device attached to the user's back. Once activated, the shield stays in place and seems to operate without a visible emitter of any kind. Like the Bubble Shield, the Drop Shield resembles a geodesic dome, made of tessellating hexagons.
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