Among the comments the US Food and Drug Administration (“FDA”) received on regulations on Substantial Equivalence (“SE”) and Hazardous and Potentially Hazardous Constituents in Tobacco and Smoke (“HPHC”), there were two that suggested that the mainstream smoke (“MSS”) from smoking articles made from roll-your-own (“RYO”) products (RYO includes tobaccos, rolling papers, and tubes with and without filters already incorporated in them) be tested for HPHC. Perhaps the writers envisaged such requirements could be bad for producers of RYO products given the known difficulties and costs of getting even MSS “tar” and nicotine determined on RYO products. Perhaps they also considered the difficulties in using the applicable ISO Standards (ISO 15592-1:2001, 15592-2:2001, 15592-3:2008) to fabricate smoking articles from RYO products available to most US consumers. ISO 15592 was developed with tubes and tobaccos used in Europe. Typical US tubes are larger in diameter (~8.1 mm versus ~7.2 mm, both 70 mm tobacco column) and some popular US RYO contain high amounts of expanded tobacco (“ET”, as determined by solvent flotation) while the tobacco blends used to develop the ISO standard did not contain ET. Based on the formula given in ISO 15592-3:2008, US tubes require a tobacco weight of 950 mg versus 750 mg required for the European tubes (tobaccos conditioned at 75% RH, calculated tobacco density ~ 265 mg/cc). Several different filter tubes were evaluated using a Top-O-Matic maker along with four types of tobacco [high ET RYO (sold with rolling papers), tube-cut containing ET, cigarette-cut without ET, and traditional European fine-cut (sold with rolling papers). Smoking articles complying with ISO 15592 could not be made reliably with the high ET RYO blend.