Housed in a plastic container, the bomb has a metal partition that separates two liquid reagents. Once the partition is removed, the liquids mix and react, causing them to rapidly expand and then solidify, creating a physical barrier blocking the tunnel.  The device is either set at its target by an individual or thrown.
In 2021, testing of sponge bombs was reportedly conducted by IDF in simulated tunnels. 
During initial testing of these bombs, the liquid emulsion was found to be hazardous to work with when mishandled – some Israeli soldiers lost their eyesight.