A thermal bag is a soft-sided carrier that slows heat transfer between the product and its surroundings, and it has three layers: the outer face is the first defence against impact and water, the insulation delays heat coming in, and the inner face decides cleaning and leak handling. Putting an ice pack inside does not turn it into a cooler; if the product goes in at the wrong temperature, the bag cannot correct it on the road.
Where does the limit begin?. On a short single-drop run a bag may be enough. On a route where it is opened again and again, carries weight on top or is washed every evening, the zip, the seams and loss of shape turn into temperature loss. ATP also defines insulated equipment by rigid insulating walls, doors, floor and roof; a soft bag falls outside that class, and this is where a rigid insulated container takes over.
Before buying, test the bag in your own work:
- Pick the hardest route: the longest one or the one opened most often.
- Load it with the real product at the real fill level.
- Write the starting and delivery temperatures, the number of openings and the waiting times on one form.
