When a cooler bag disappoints, the insulation is rarely the culprit. The openings are.

The zip

A zip runs the full width of the bag and is, thermally, a slot. Warm air moves through it constantly.

An insulated flap folded over the closed zip removes most of that, and its absence is the single most common reason a bag underperforms its foam.

The seams

An unbound seam is a continuous path from the inside surface to the outside one, all the way round the bag.

Taped or bound seams break that path. Again: cheap, invisible, and the first thing removed.

The load and the ice

A cooler does not make anything cold. It slows down what is already cold getting warm, and ice or packs are the actual reservoir.

A bag packed with warm cans and one small pack will disappoint whatever it is made of, which is why any honest duration figure has to state the load.

The size, which surprises people

Small bags lose cold fastest because they have more outside surface per unit of contents.

A lunch bag holding for four hours is doing a harder job than a family cooler holding for eight.