Styles of the late 20th century have largely been derived from the current world architectural trends, or have been imitative of previous Australian styles. These styles include Stripped Classical, Ecclesiastical, International, Organic, Sydney Regional, Perth Regional, Adelaide Regional, Tropical, Brutalist, Structural, Late Modern, Post Modern, Australian Nostalgic and Immigrants' Nostalgic. In the 1980s and 1990s most parts of Australia had a building boom which strained building supplies, so many buildings from this era are characterised by cheap and low quality materials.