The three levels
Institute Cargo Clauses A, B and C
Almost every marine cargo policy in the world is written on one of these three, and the difference between them is not a matter of degree. (A) is all risks with stated exclusions. (B) and (C) are lists, and if your loss is not on the list it is not covered.
ICC (A)All risks
Covers physical loss or damage from any external cause, except what the policy specifically excludes. The burden sits with the insurer to point at an exclusion rather than with you to prove your loss was on a list.
What it addsTheft, non-delivery, handling and stowage damage, breakage, and the large category of things that go wrong without anyone being able to say exactly what happened.
Use it whenThe default for manufactured consumer goods. If you are reading this page to decide, this is almost certainly the answer.
ICC (B)Named perils, wider
Covers a defined list of events. If your loss is not on the list, it is not covered, however unfair that feels.
What it addsOver ICC (C): earthquake, volcanic eruption and lightning, water entering the vessel, container or place of storage, and total loss of a package lost overboard or dropped while loading.
Use it whenOccasionally sensible for robust, low-value, hard-to-damage cargo where the premium difference is material.
ICC (C)Named perils, minimum
The narrowest cover in normal use, and the level a seller is obliged to provide under CIF. Broadly: catastrophes to the vessel itself.
What it addsFire or explosion, the vessel sinking, grounding, stranding or capsizing, collision, derailment or overturning of a land conveyance, discharge at a port of distress, jettison, and general average sacrifice.
Use it whenRarely the right choice for finished goods, and frequently mistaken for real cover because a CIF seller's certificate arrived.
Peril lists above are the standard clause structure and are given so you can tell the tiers apart. Individual policies vary, and the wording on your certificate is what actually governs. Read it, and specifically check which of the three you have been sold.