The materials batch of the composting experiment containing the compostable plastics was regularly sampled during the process. These sampling was done using the standardized method NF EN 12579:(12579:2013, 2013). For a batch of compost (max 580 m³) it recommends taking 12 elementary samples, each weighing 1 kg, from various locations. The quartering method described in ASTM C702/C702M:2018 (C702/C702M:2018, 2018) was used to reduce the sample size without creating a systematic bias due to product heterogeneity and obtain a representative final sample of around 10 kg per batch and per sampling time. All the compost samples were air-dried. They were then passed through a series of sieves with decreasing mesh sizes to obtain eight fractions ranging from 10 mm to 0.2 mm. Each fraction was weighed, and its water content was determined.