What does Xen smell and feel like?

I don't think Xen is actually in a vaccume, so much as the air just has a lot of alien chemicals and viruses that are dangerous to humans. So we have to wear a helmet in Xen, meanwhile the Xen flora and fauna is far hardier, so they aren't bothered by our silly planet.

Still, is Xen's ground fleshy or sticky? Since HL:A depicts it as almost alive, in a sense