Built-in ice packs are a gimmick. Get a proper insulated cooler.

If you need food cold for 8 hours, skip the lunchboxes with glued-in ice packs and buy a decent insulated cooler instead.

The ice pack matters way less than the insulation. Those lunch bags with a sewn-in gel pack are fine for a few hours. After that, heat leaks through the thin walls and the gel pack turns into a lukewarm puddle. For a full work day, you need thick foam walls, a zipper that actually seals, and a leakproof lining. That keeps the cold in — the ice pack just supplies the cold.

Also, built-in packs eat up space. A pack that covers the entire bottom of the bag is taking up room that could hold an extra yogurt or a can of soda. You’re better off with an empty, well-insulated bag and a removable ice pack. Or just freeze a water bottle. It works just as well, and you get drinking water after lunch.

If you really want a lunch box with a built-in pack, look for one with a removable pack and walls at least an inch thick. Otherwise, grab a small soft cooler from a brand that actually makes coolers, not backpacks. Test it once at home with a thermometer. That’ll tell you more than any marketing claim.

Your sandwich shouldn’t be a science experiment.