Durium Junior was a flexible single-sided 4-inch phonograph disc made from Durium (a synthetic brown resin invented in the US in 1929) with a cardboard backing. These were introduced in 1931 by the Durium Products Corp. who also made the 10-inch Hit Of The Week phonograph records in the US.
The Durium Junior mostly offered advertising and music combined though some were just music, and they played for around one and a half minutes. The format was also used for some childrens records.
The last Hit Of The Week release was in June 1932 and Durium Records in the UK ended production in January 1933. It’s unclear when Durium Junior ended, but it was likely around the same time.