When December rolls around, we find ourselves asking the same questions: What’s in figgy pudding? Why do I need to make the Yuletide gay? And what is tinsel exactly?

That last question is only slightly less mystifying than the first two. Many of us have seen tinsel—if not in person, then in one of the countless holiday movies and television specials that air this time of year. It’s the stringy, shiny, silvery stuff that’s hung up as decoration, primarily on Christmas trees. But what is it made of? And why is it associated with the holiday season? This is where the seemingly simple decoration gets complicated.

Tinsel is one of the cheaper items used to trim trees today, but that wasn’t always the case. In 17th century Germany, the first Christmas trees were embellished with tinsel made from real silver pressed into strips. These early Christmas trees were also decorated with real, lit candles, and the silver combined with the flickering firelight created a twinkly effect that worked as a precursor to modern-day string lights.

Silver tinsel did have its drawbacks. It was expensive, so only the wealthiest families had access to it. And those who did have enough money to own tinsel had a limited window to use it, as the metal often tarnished before December 25.

By the early 1900s, the Christmas traditions imported by German immigrants had become mainstream in the U.S. Americans were looking for affordable ways to beautify the evergreens in their living rooms, so manufacturers started making tinsel out of aluminum and copper. The updated decorations produced the same festive sparkle as the silver versions, but for a fraction of the price; also, they could be reused year after year. But they weren’t perfect: The aluminum paper in tinsel was extremely flammable, making it a disastrous choice for dry trees decorated with lights. When World War I began, copper production was funneled toward the war effort and tinsel disappeared from holiday displays.

Its absence turned out to be temporary. Despite centuries of hiccups, makers of holiday decor still believed tinsel deserved a place in modern Christmas celebrations. They just needed to come up with the right material to use, something that could be hung in every home without any backlash. In the early 20th century, the clear choice was lead.

Lead revived tinsel from obscurity, and soon it was embraced as a standard Christmas component along with ornaments and electric lights. It became so popular in the 1950s and ‘60s that tinsel is often thought of as a mid-century fad rather than a tradition that’s been around as long as Christmas trees themselves.

With so many synthetic decorations becoming available around Christmastime, tinsel made from metal was considered one of the safer items to have in the home. A 1959 newspaper article on holiday safety reads: “Tinsel is fairly safe, because even if kiddies decide to swallow it, it will not cause poisoning.”

As we know today, tinsel made from lead isn’t “fairly safe.” Lead that gets ingested or absorbed through the skin can cause headaches, vomiting, constipation, and in extreme cases, brain and kidney damage. Young children are especially vulnerable to lead poisoning.

In the 1970s, the U.S. government started setting limits on how much lead can be in consumer products, and in 1972, the FDA came to an agreement with tinsel manufacturers that production of the lead product would cease.

It may not be as en vogue as it was 60 years ago, but tinsel still resurfaces every holiday season. So if the tinsel we use today isn’t made from silver, copper, aluminum, or lead, what is it? The answer is polyvinyl chloride. Industrial machines shred shiny ribbons of the plastic to make the wispy strands that add a bit of glamour to Christmas trees. Plastic tinsel isn’t as elegant as the kind made from real metal, and it’s lightweight, so it’s less likely to stay put after it’s hung over a pine branch. For these reasons, PVC tinsel never caught on to the degree of its predecessor, but it still succeeds in bringing vintage bling to the holidays without poisoning your family.