Steam is the enemy. Let it breathe before you wrap it.

Pack a grilled cheese hot and wrapped tight and you’re basically steaming it into a sad, soggy mess — so the trick is letting it vent, then insulating.

First: don’t wrap it while it’s screaming hot. Give it 2-3 minutes on a wire rack (or just on the cutting board, flipped once). That lets the steam escape instead of condensing back into the bread. This is the step everyone skips and it’s the whole ballgame.

Then wrap it in paper — parchment or a paper towel, not plastic wrap. Paper absorbs a little moisture and lets the rest escape. If you need it warmer for longer, wrap the paper-wrapped sandwich in foil, but leave one end slightly open, or poke a couple holes. Then stick that in an insulated lunch bag with a thermos or hot pack next to it.

If you’re using foil alone, don’t. That’s a steam tent. The bread will survive maybe 20 minutes before it turns into a sponge.

Fifteen minutes is the realistic window. You can stretch it to an hour with the paper-towel-plus-insulated-bag method, but it won’t taste just-off-the-griddle. That’s physics, not a failure on your part.

Make two. The second one is your test run, and you deserve a crispy one.