Many polymers are hygroscopic, meaning they absorb water from the surrounding air. Absorbed moisture acts as a plasticizer, reducing the glass transition temperature ( Tgcap T sub g
For global manufacturers, understanding the difference between ASTM and ISO standards is crucial. The ASTM D618-21 PDF contains a direct note comparing it to . Both standards address the conditioning of plastics; however, they differ in technical content. The note explains that ISO 291 describes only two temperature and humidity conditions for conditioning or testing, whereas ASTM D618-21 provides a broader, more flexible framework. This distinction is vital for companies shipping products to different regulatory regions. astm d61821 pdf