No-ice-pack lunch boxes are a gimmick. Get an electric one instead.

An electric lunch box is the only realistic way to keep food cold for 8 hours without ice packs.

Insulation doesn’t create cold. It just slows down warming. So any passive bag, even a $100 one, needs something cold inside to do the work. Without ice packs, you’re just putting warm food in a thermos and hoping. That’s not going to hold below 40°F for a full workday.

Your options:

• Electric thermoelectric cooler/lunch box. Plugs into USB or 12V. Active cooling, works without ice. Downsides: you need a power outlet or power bank, and some models struggle in hot offices.
• Fake “no ice pack” hack. Freeze a water bottle, or use frozen grapes/berries to pack around the food. Works, but that’s still an ice pack, just with better PR.
• High-end cooler-style lunch box. Something like a Yeti or a rotomolded cooler. Still needs pre-chilled food and a tight fill to stay cold. I wouldn’t trust it for 8 hours unless the food starts near freezing.

If you truly refuse to use ice packs, buy an electric one. Otherwise, save your money and just use a freezer pack in a decent insulated bag.

Physics always wins. You need cold mass or electricity.