3M, Aearo Lose Delaware Appeal on Earplug Insurance Coverage

3M Co.'s legal defense payments in product liability litigation over Aearo Technologies LLC’s combat arms earplugs failed to trigger insurers’ coverage obligations, Delaware’s high court ruled.

3M, Aearo’s parent company, wasn’t a named insured party on Aearo’s policies, so its payments toward defense costs and legal fees in the earplug litigation—which it said have exceeded $370 million—couldn’t satisfy Aearo’s self-insured retention requirements, Delaware Supreme Court Justice N. Christopher Griffiths wrote for the majority Tuesday.

The ruling marks the latest setback for 3M and Aearo, which faced multidistrict litigation comprising more than 280,000 lawsuits at its peak as well as additional ...