I disagree. Not that they can’t tunnel around it given enough time, but it is tactically useful in that a foam-closed cross tunnel can be safely ignored by intruding IDF troops on a patrol and they don’t have to leave troops behind at every cross tunnel to keep an eye on it. By the time Hamas can bypass it (and it will be a while if these tunnels are lined with concrete as reported) the IDF force that deployed it won’t be there - it’s highly useful on a short term tactical basis.
They shouldn’t be down in the tunnels. We didn’t send Marines crawling through every tunnel on Peleliu. Isolate and seal and starve. Every time an entrance is found, flood them with seawater, hit them with deep penetrating massive bombs, liberal use of napalm, poison gas, pump full of propane and detonate.
Actually, drill a deep hole and do a small underground nuke. I have stood on a plowshares site in Northern New Mexico and without the sealed wellhead and marker you’d never know. It shouldn’t make fallout or a crater if you plan it right.