AO31 density?

I've received questions about the density of polyvinylcaprolactam (polyvivo AO31). Previous publication (listed below) has listed the density of polyvinylcaprolactam as 1.3 g/cm3:

Imaging and density mapping of tetrahydrofuran clathrate hydrates by phase-contrast x-ray computed tomography
Takeya, Satoshi and Honda, Kazumasa and Kawamura, Taro and Yamamoto, Yoshitaka and Yoneyama, Akio and Hirai, Yasuharu and Hyodo, Kazuyuki and Takeda, Tohoru, Applied Physics Letters, 90, 081920 (2007), DOI:http://dx.doi.org/10.1063/1.2709645