Your lunch box can survive the washer. The dryer will kill it.

You can machine wash most fabric insulated lunch boxes, but the heat from the dryer is what wrecks that heat-sealed lining and waterproof coating.

Cold water, gentle cycle, mild detergent. Turn it inside out first if the shape allows it. That’s about as risky as it gets — the water itself isn’t the enemy.

The enemy is heat. Hot water can soften the adhesive that binds the lining, and the dryer will outright melt it. That’s why you see the inner foil peeling and bubbling in sheets. That’s not wear and tear. That’s someone ran it through the dryer.

So: wash cold, then hang it to dry. Leave the flap open, maybe stuff a towel inside to hold the shape. If it still smells funky after washing, wipe the inside down with a vinegar-water mix before you toss it in, or do a baking soda soak.

One warning: if the lining is already peeling or cracked, skip the machine entirely. The agitation will peel it off faster. Hand wash that one gently and accept it’s on its way out.

Air drying takes overnight. That’s the whole trick. Your lunch box will be fine.