Research has shown that deacidifying agents are effective in reducing the degradation of new cellulosic textiles as well as paper, however, conservators are hesitant to deacidify historic textiles. This research addresses their concerns about possible changes in fabric properties if historic textiles are deacidified. The effect of magnesium bicarbonate, calcium hydroxide, and methoxy magnesium methyl carbonate (Wei T'o solution #2 and #12 spray) on physical properties has been studied. Researchers deacidified 13 naturally aged cottons and linens, seven commercially dyed cottons, and three cottons artificially aged by bleaching and ionizing radiation. Color change was minimal on the naturally aged cottons and dyed cottons, but the artificially aged cottons darkened noticeably. Moisture regain increased by 0.2 to 0.4% and weight gain was 2 to 5%. When four treated fabrics were subjected to accelerated aging at 100°C, and 100% relative humidity for 15 days, the pH of these fabrics stayed above 6.6, while untreated specimens became noticeably acidic (pH 3.8-5.1). Fabrics stiffened considerably particularly when immersed in Wei T'o #2, but the stiffness did not reduce the flex abrasion of old fabrics. Scanning electron microscopy (SEM) photomicrographs show that the surfaces of fibers are essentially unchanged, but some fibers have adhered together. New methods of application are required to reduce stiffening.