U.S. Application No. 13/652,858, directed to high density polyurethane construction boards.

“Said coverboard having a density greater than 2.5 pounds per cubic foot and less than 6 pounds per cubic foot” is in claim 1 (page 3).  Prior art G has a coverboard of 6-25 pounds per cubic foot, preferably 8 (pages 3-4).  Prior art L teaches  0.5-10, preferably 1-5, for a material (page 4).  The Examiner notes that prior art G teaches that fillers in the coverboard may cause variations in density and that prior art L teaches material that could be used with a density in the recited range, alleging it as a design choice to use the material and density of prior art L in the coverboard of prior art G  and/or margin of error by the slightest percentage (pages 4-5).  The Federal Circuit indicated that prima facie obviousness is established where the difference in a range is virtually negligible (less than 6 verses 6 pounds per cubic foot) (page 9).  This shifted the burden to applicants to show unexpected results or criticality, which was not done (pages 9-10). 

Hindsight: When claiming a range, try to choose the ranges based on a reason.  This may make a showing of criticality or unexpected results easier.  Use nested or varying ranges to allow for claiming a range spaced from any unknown prior art.  Of course, such varying ranges may detract from the indication of criticality.