The project at the Prado museum in Madrid involved 252.6m3 of wood, of which 58% (148.4m3) came from verified Forest Stewardship Council certified sources.

The Rainforest Alliance, which hailed the extension as the biggest Spanish use of certified timber to date, said a temporary union of construction companies, UTE El Prado, working on the project had led the trend towards sustainable timber sourcing in Spain. Timber used included oak, birch plywood, yellow pine and beech.