Tinsel dates back to 1610 to a place in Nuremberg, Germany, where thin strands of real silver were used to decorate trees and reflect candlelight, as they would often put real candles in their trees (fire hazard!). Silver was not cheap so the use of tinsel was a sign of wealth.
However, silver tarnishes quickly, meaning it would lose its shiny appearance. other metals were tried such as copper and tin. These metals were also cheaper, so it meant that more people could use them, but in 1914, because of WWI, all copper was used in the war effort. A substitute was needed. Aluminium was used, but this caused fire scares. Lead was used, but that was toxic.
Contemporarily, tinsel is made from polyvinyl chloride, or PVC, which is given extensive treatment to make it shiny.
https://www.bbc.co.uk/newsround/42313813
