With U.S. Treasuries largely rallying last week amidst the equity markets’ turmoil (with the exception of Friday where we saw Treasuries actually give back some gains), related exchange traded funds tracking fixed-income markets have been exceptionally active.

Two reasonably “new” ETNs that debuted last fall have caught the market’s attention recently and have exhibited an increase in trading volume as well as assets under management.

The iPath U.S. Treasury Flattener ETN (NYSEArca: FLAT) surged last week amidst the run up in Treasury prices. [What Now for Treasury ETFs After Downgrade?]

FLAT is designed to capture returns that become available in a U.S. Treasury yield curve environment by “steepening” or “flattening” the U.S. Treasury yield curve.

The index will increase in response to a “steepening” of the yield curve and decrease in response to a “flattening” of the yield curve.