This story originally appeared on ETFdb.com. ETFs have emerged as popular tools for establishing exposure to a wide variety of asset classes, ranging from U.S. Treasuries to Vietnamese equities. But few corners of the exchange-traded product world have seen more explosive growth in recent years than precious metals, as investors have embraced these vehicles as the most efficient way to access assets that have turned in some monster performance numbers in recent years. The 21 ETFs in the Precious Metals ETFdb Category have more than $83 billion in aggregate assets, representing about 8% of the total ETP industry. That’s a massive total for an asset class that generally accounts for a relatively minor portion of long-term portfolios, reflecting the appeal of the low maintenance and low fees offered by the exchange-traded structure.