low void volumes can be produced. The thermal properties of the polymer are surprisingly good. The organic polyisocyanate preferably has an average functionality about 1.9 to 4, and more preferably 2.0 to 3.0, 2.0 to 2.5 or 2.0 to 2.3. In some embodiments, the average isocyanate equivalent weight can be from about 80 to 250, more preferably from 80 to 200 and still more preferably from 125 to 175. The organic polyisocyanate can be aromatic, aliphatic and/or cycloaliphatic. Examples of polyisocyanates include m-phenylene diisocyanate, 2,4- and/or 2,6- toluene diisocyanate (TDI), the various isomers of diphenylmethanediisocyanate (MDI), hexamethylene- 1,6-diisocyanate, tetramethylene- 1,4-diisocyanate, cyclohexane- 1,4-diisocyanate, hexahydrotoluene diisocyanate, hydrogenated MDI (Hi2 MDI), naphthylene- 1,5-diisocyanate, methoxyphenyl-2, 4-diisocyanate, 4,4’- biphenylene diisocyanate, 3,3’-dimethoxy-4, 4’ -biphenyl diisocyanate, 3,3’- dimethyldiphenylmethane-4, 4’ -diisocyanate, 4,4’,4”-triphenylmethane tri- isocyanate, polymethylene polyphenylisocyanates, hydrogenated polymethylene polyphenylisocyanates, toluene-2, 4,6-triisocyanate, and 4,4’-dimethyl diphenylmethane-2,2’,5,5’-tetraisocyanate. Preferred polyisocyanates include MDI and derivatives of MDI such as biuret-, uretonimine- and/or carbodiimide- modified “liquid” MDI products and polymeric MDI. “PolymericMDI”is a mixture of MDI (any isomer or mixture of isomers) with one or more polymethylene polyphenylisocyanates that have three or more phenylisocyanate groups. The “PolymericMDI”may have, for example, an isocyanate equivalent weight of 126 to 160 and a number average isocyanate functionality of 2.06 to 3.5, especially 2.2 to 3.2 or 2.2 to 2.8. The “liquid” MDI may have an average functionality of 2.01 to 2.2 and an isocyanate equivalent weight of 126 to 150, especially 140 to 150. A mixture of two or more organic polyisocyanates may be used. The polyols b) include b-1) one or more polyols having a hydroxyl equivalent weight of greater than 260 g/mol and a nominal hydroxyl functionality of 2 to 4. In some embodiments, a polyol b-1) may have a hydroxyl equivalent weight of at least 400, at least 450, at least 500, at least 700 or at least 900, and up to 5000, up to 4000, up to 3000, up to 2000, up to 1500 or up to 1200. The nominal hydroxyl functionality of a polyol b-1) in some embodiments is 2 to 3.