Any spacecraft planning to spend time in the atmosphere will need to cope with hurtling clutter or be quickly destroyed. To deal with micrometeoroids (objects smaller than 10cm) shields are a necessity. For decades, the ISS and others have relied almost entirely on the Whipple shield
: a multi-layered armor that absorbs the impact of small debris.
But a new shield type may soon join the armory: metallic foam. Consisting of solid metal with a high volume of open-cell, gas-filled pores, these low-density materials are advantageous for their lightweight cellular structure relative to other shield types.
Want NASA-quality protection for your skull? Metal foam in a closed-cell conformation is also used in bicycle helmets.