Two phosphate-bonded investments that were pured into molds of a duplicating gel and a poly(vinyl siloxane) duplicating medium were examined for surface hardness. Untreated surfaces were also examined by the confocal microscope and the scanning electron microscope. The Brinell hardness of samples poured in poly(vinyl siloxane) was greater than that of the same investment poured in duplicating gel. Investments were hardest at set and were significantly softened by drying. Cast hardeners achieved some rehardening of the dried investment samples. Microscopic examination of the investment surfaces revealed greater surface irregularity of samples poured in duplicating gel than in poly(vinyl siloxane), particularly in one investment.