The units are made of powder-coated steel with glass shelves.
Here's some more information from Sander Mulder:
In a few decades our whole world economy has become reliant on the containerization of our supply lines. Known the world over for its indestructible appearance and boxy look, the shipping container is one of the best known industrial archetypes.
This modular storage system is inspired by the wonderful colour mosaics that sprout to life in every harbor and container terminal the world around.
The individual pieces can be stacked and rotated around in endless (colour-) combinations, to create your personal container terminal for all domestic storage uses.
Colour(s): available in all RAL colours.
Dimensions (HxWXD): Small:50x100x50cm, Medium:100x100x50cm, Large:200x100x50cm.
Weight: Small: 40kg, Medium: 90 kg, Large: 120 kg.
Material: powder coated steel, stained glass.
Design: Sander Mulder.