Lorica is synthetic leather. Manmade, and completely artificial! 

"Lorica is a hi-tech material created from a remarkable combination of extremely thin microfibres.  This interlacement of microfibers, soaked in special resins, has a microporous structure which is very similar to the collagen of natural skin.  This gives Lorica excellent softness, durability and breathability." -Sidi Care Brochure

Sidi, like many other brands such as Alpinestars and Dainese are incorporating Lorica in their street and race motorcycle boots.  You can't really tell the difference, as they look and feel just like boots made of cowhide. I would never know the difference just by looking. 

For some reason, I thought that Lorica wouldn't stretch out as much as cowhide, but it seems the opposite is true. 

In reviewing the Fusions, I found that they stretched out quite a bit. I'm looking forward to breaking in a new pair of Vertigo Leis, to see how much they give and perform, especially under hotter riding conditions.