It's one of the most abused terms in sustainable packaging marketing. Here's the actual test.
"Marine-degradable" is a testable, specific claim with a real methodology behind it — which is exactly why it's also one of the most commonly misused terms in sustainable-packaging marketing, since almost nothing about the phrase stops a manufacturer from using it without ever running the test.
The recognized method is ASTM D6691, "Standard Test Method for Determining Aerobic Biodegradation of Plastic Materials in the Marine Environment." It exposes a material to a defined population of at least ten aerobic marine microorganism genera and measures the CO₂ produced as the material's carbon content is metabolized. To pass, at least 60% of the material's carbon must convert to CO₂ within 180 days at 30°C [1]. Notably, there is no equivalent ISO standard — ASTM D6691 (or the closely related ISO 22403/23832 family) is effectively the reference method globally.
Under the MPFREE Standard, a degradability claim on packaging is certified only against real third-party test data from a method like this — never accepted on the strength of the material's design specification or the manufacturer's own internal testing.