Thermally insulating foam with vertically elongated cells

An extruded polymer foam, the foam comprising a polymer matrix defining cells therein wherein the foam is characterized by:

• (a) the polymer matrix comprising styrene-acrylonitrile copolymer and 0.1 to 10 weight-percent infrared attenuator, based on foam weight, dispersed in the polymer matrix;
• (b) the cells having average sizes in the foam vertical, horizontal and extrusion directions, as determined by ASTM D-3576, such that
• i. the average size in the foam's vertical direction of 150 micrometers or less;
• ii. the ratio of average vertical direction cell size to average extrusion direction cell size that is greater than one;
• and
• iii. the cell anisotropic ratio that is greater than 1.1;
• (c) having a P-Ratio of 0.7 or less, with compressive strength values determined according to ASTM D1621;
• (d) having less than 0.2 moles of hydrocarbon blowing agents in the cells per kilogram of foam as determined by gas chromatography;
• (e) having a density of 20 to 48 kilograms per cubic meter as determined by ASTM D1622;
• and
• (f) having an average 25-year thermal conductivity that is 0.030 Watts per meter-Kelvin or less when free of fluorinated blowing agents and less than 0.028 Watts per meter-Kelvin when containing fluorinated blowing agent, with 25-year thermal conductivity as determined by the slicing technique of EN13164.