This is the one piece of advice that costs people money in the wrong direction. Someone has an unpleasant experience with warm food, concludes the bag was not good enough, and buys a more expensive one. The bag was almost never the problem. The car was, and the more expensive bag will fail in exactly the same place.
What actually happens inside a parked car
A closed vehicle in the sun behaves like a glasshouse. Sunlight passes through the windows, is absorbed by dark seats and dashboards, and the heat cannot escape. The interior climbs far above the outside air temperature and keeps climbing, and it does so within a surprisingly short period rather than over the course of a whole afternoon.
Insulation only slows a gradient it can cope with
Insulated fabric works against a modest difference between inside and outside. Put the same bag in an environment that is dramatically hotter than a summer street and the maths changes completely. The ice pack thaws far faster, and once it is liquid the bag is simply a padded container full of warm food. Anything at https://mexsus.com/ will behave the same way, because physics does not care what you paid.
The boot is not a safe compromise
People assume the boot is cooler because there are no windows. It is out of direct sun, which helps a little, but it is a sealed metal box attached to a vehicle absorbing heat all over. On a hot day it is still far warmer than any room in your house, and it has poor airflow, so it holds that heat long after you park in the shade.
What to do instead of upgrading
The fix is behavioural and free. Take the bag with you. If you are shopping, do the chilled aisle last and drive straight home. If you are working from the vehicle, keep the bag in the cab with the air conditioning rather than in the boot, or move it inside a building when you stop.
- Carry the bag in with you rather than leaving it in the vehicle
- Park in shade when you have no choice, and use a windscreen shade
- Buy chilled items last and drive home directly
- Never store a lunch in the car overnight for the next day
- If the packs have fully thawed and the food is warm, do not eat it
Where money is genuinely worth spending
A better bag does help in the situations where insulation is the limiting factor: a long walk to a picnic spot, a shaded campsite, a train journey, a shift in a cool store room. If those are your scenarios, thicker insulation and a better closure earn their keep. If your scenario is a car in a car park, they will not.
The one case where a car cooler makes sense
Powered coolers that plug into the vehicle are a different product entirely, because they actually remove heat. They are bulky, they draw current, and they are overkill for a packed lunch. For long transport of chilled goods in a hot climate they are the honest solution, and no passive bag substitutes for one.
Judge the outcome, not the receipt
If your food arrives warm, work out which link in the chain failed before you replace anything. Nine times out of ten it is a parking space, an hour in the sun, or a pack that was never frozen solid. Replacing a functional bag will not repair any of those.