Silver is one of this year's best-performing commodities, but that is not motivating investors to nibble at silver exchange-traded funds (ETFs). Even as the iShares Silver Trust (SLV), the largest silver-backed ETF trading in the U.S., soars, it is actually bleeding assets. Year to date, SLV is up 13.7 percent, or nearly 270 basis points ahead of the largest gold-backed ETF. However, investors have yanked $222 million from SLV while pouring more than $1.1 billion into the SPDR Gold Shares (GLD). Actually, investors have pulled money from SLV for seven consecutive months, reports Bloomberg.

One silver ETF that has been attracting assets is the PureFunds ISE Junior Silver (SILJ). SILJ is lagging silver with a gain of just over 7 percent year to date, but investors have poured $15.7 million of new money into the small-cap silver ETF. SILJ, which is just over four years old, tracks the ISE Junior Silver (Small Cap Miners/Explorers) Index. The ETF holds 24 stocks, but investors should be aware that it is top heavy, as just three stocks – Pan American Silver Corp. (PAAS), Coeur Mining, Inc. (CDE) and First Majestic Silver Corp. (AG) – combine for about 41 percent of the ETF's weight. (See also: Hi-Ho, Silver! Hot Silver ETF Soars Again.)

While $15.7 million may not sound like much, it is a decent chunk of the nearly $70 million currently residing in SILJ. There are some factors at play that could prompt some traders to turn to SILJ for small-cap mining exposure. For example, it was reported last week that the popular VanEck Vectors Junior Gold Miners ETF (GDXJ) is perhaps getting too big for its index and that the index is being adjusted to prevent problems. Additionally, the Direxion Daily Junior Gold Miners 3X Shares (JNUG), the triple-leveraged answer to GDXJ, has temporarily suspended creations of new shares. SILJ is not a leveraged ETF, nor is it a gold miners fund, but its penchant for big intraday moves can make it a suitable replacement for active traders seeking junior miners exposure. (See also: Top 5 Gold ETFs for 2017.)

Plus, there are encouraging signs from professional traders that they are betting on more upside for silver, which can translate to gains for SILJ. "Money managers boosted their net-long position, or the difference between wagers on price gains and bets on declines, by 5.5 percent to 98,845 futures and options in the week ended April 11, the highest in U.S. government data going back to 2006," according to Bloomberg. (See also: Top 3 Silver Stocks for 2017.)

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