Sheet metal and other thin materials are cut with power shears and nibblers in straight or curved cuts. Sheet metal shears cut flat or corrugated panels and ducts by pivoting the pivoting blade against the fixed blade. They take longer to cut than nibblers, but the results are smoother edges and less mess. Sheet metal nibblers cut flat, corrugated, or uneven sheets by punching a succession of small holes. They cut tighter curves and more exact corners than shears, but they leave shavings and rough edges. Carpet and leather shears slice through carpet, leather, cardboard, and other soft materials by rolling their circular blade along surfaces. Cement board shears slice through fiber cement siding and sheets like scissors.