model -> G-code = hollow walls. what am I doing wrong?

[avocadobaby]

I made a cylinder in rhino5 with a wall thickness of 1.1mm It seems pretty solid and looks normal, but when I go to print it looks (and prints) hollow with no end caps both in makerbot and simplyfy3d. I havn't tried RepG but I imagine it is the same.
I have set the infill to 100% with no change.

any ideas?

image:
top left=simpl3d
top right= simplify3d preview mode
bottom left = rhino5
bottom right = makerbot toolpath visualisation
images.jpg