Values of HLB < 9.0 indicate a lipophilic character while HLB > 11.0 is assigned to hydrophilic excipients. The range of 9.0 -11.0 is considered intermediate . . Although Acconon C44 EP/NF ® , Gelucire ® 50/13 and PEG showed better solubilization capabilities for BTB, these excipients were not employed as solid and liquid lipids, in the NLC core. Since the solid lipid was already defined as cetyl palmitate, a common excipient used in NLC preparation , the liquid lipid should be lipophilic enough to have affinity with it, i.e., to avoid phase separation. Among the excipients with high solubilization capacity, Capryol ® 90 was found to be an interesting option. Capryol ® 90, or propylene glycol monocaprylate, is a nonionic water-insoluble surfactant that can be used as co-surfactant in oral lipid-based formulations, or co-surfactant and solubilizer in topical dosage forms. Therefore, Capryol ® 90 was selected considering BTB solubility and its possible affinity with cetyl palmitate, considering its lipophilic character. Dhaykol 6040 LW was selected for comparison, as an excipient of low solubilization capability for BTB. Transcutol ® HP was not chosen because its low miscibility with the selected solid excipient, as described in previous papers .