In the mesh bag results, the fiber-based items tend to show lower disintegration / higher residuals than biopolymer products. This is consistent with other field testing results led by other organizations.
Although more research is required to have decisive answers to this question, there are early signs in the data that moisture and agitation are crucial for fiber breakdown. Thus, since the mesh bag method exposes test items to little to no agitation, the method itself could actually inhibit fiber breakdown.
Another factor is trial duration. Many facilities operate on increasingly shorter timeframes, as short as 30 days or less, when compost is still quite hot. However, fiber is broken down mostly by fungi, which thrive at lower temperatures that generally come after the initial phase of composting. If a facility is screening before curing, or if a field test ends before the fungal communities proliferate, the fiber products will not have been exposed to the conditions important for their breakdown, leading to high residuals left over.