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Several factors were investigated that affect porous strut morphology in the Highly Porous Supersoft Viscoelastic Foam. Porous strut morphology and high air permeability of the Swiss-Cheese TDI VE technology were found to be enabled by the combination of immiscible polyether polyols mixed with a third, highly hydrophobic polyol of high equivalent weight that is immiscible with either of the first two polyether polyols. Completely "punctured through" pores in struts were observed more frequently in foam samples where an isocyanate index of 90 versus 100 was employed. When isocyanate index is fixed to 90, it was found that a poly(1,2-butylene oxide) ("PBO") monol level of !3.0 parts per hundred polyol (pphp) was needed to see the first signs of a "punctured" pore strut morphology. Studies show that a "high-Eq.Wt.-hydrophobic-polyol-leaving-voids" model is consistent with observed results. Hydrophobic polyols that allowed the formation of porous strut morphology included BO-4000 monol (Eq.Wt. $ 4000) and PBD-10000 diol (Eq.Wt. $ 5000). The use of these hydrophobic polyols also yielded air flows that were significantly higher than those obtained with the "standard" viscoelastic foam formulations that were prepared at the same isocyanate index. V C 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44449. The difference compared with previous cell opener technology is that a combination of EO-and BO-rich polyols is used. We find porous strut morphology as the characteristic feature of the HPSVE made with TDI isocyanate. The technology is ground breaking in that the creation of a completely new cell