The sidepanels are secured by this latch,
and you can release the side panel just by pushing the latch upwards.
and the side panel comes off!
The side panel comprises of mainly aluminum, reinforced with a layer of steel, and the black stuff you see is a layer of noise insulation material added to dampen any possible noise generated by any mechanical components within the case.
Side view with the side panel removed. The black duct that you see in the middle of the case is used to channel airflow to the expansion cards within the case.