Technically it's acrylonitrile butadiene styrene (ABS). 
But yes, it's plastic! 
Don't forget it's primarily an industrial product which happens to work well (IME very well) in high-end audio to isolate a USB input from a computer/streamer.
More info: http://intona.eu/en/products
And everything one wants to know about it here as well: http://intona.eu/en/answer/1000
Edit: lots of forum chatter about it (links below copied from my system topic):
http://www.computeraudiophile.com/f6-dac...tor-26815/
http://www.xtremeplace.com/yabbse/index....=222582.30
http://www.phasure.com/index.php?topic=3297.15
http://www.whatsbestforum.com/showthread...B-isolator!
http://www.head-fi.org/t/777678/intona-h...b-isolator
http://www.superbestaudiofriends.org/ind...hizzle.62/
http://www.pinkfishmedia.net/forum/showt...p?t=182061
http://www.computeraudiophile.com/f6-dac...ead-27465/
http://www.computeraudiophile.com/f6-dac...ted-27636/
But yes, it's plastic! Don't forget it's primarily an industrial product which happens to work well (IME very well) in high-end audio to isolate a USB input from a computer/streamer.
More info: http://intona.eu/en/products
And everything one wants to know about it here as well: http://intona.eu/en/answer/1000
Edit: lots of forum chatter about it (links below copied from my system topic):
http://www.computeraudiophile.com/f6-dac...tor-26815/
http://www.xtremeplace.com/yabbse/index....=222582.30
http://www.phasure.com/index.php?topic=3297.15
http://www.whatsbestforum.com/showthread...B-isolator!
http://www.head-fi.org/t/777678/intona-h...b-isolator
http://www.superbestaudiofriends.org/ind...hizzle.62/
http://www.pinkfishmedia.net/forum/showt...p?t=182061
http://www.computeraudiophile.com/f6-dac...ead-27465/
http://www.computeraudiophile.com/f6-dac...ted-27636/
PS Audio P3, Shunyata ΞTRON Alpha Digital and HC/Furutech power cables, Paul Hynes SR7EHD-MR4, DIY Roon Server & Roon Endpoint running AudioLinux Headless, Phasure Lush^2 USB cable, Audioquest Diamond RJ/E ethernet, Uptone Audio etherREGEN, Mutec MC-3+ USB, Shunyata ΞTRON Anaconda Digital XLR AES/EBU, Devialet Expert 250 Pro CI, Nordost Tyr Reference LS cables, Von Schweikert VR-5 SE Anniversary Edition, Anti-Mode Dual Core 2.0, JL Audio Fathom F112. More detail here.
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