To investigate the effect of contoured insoles constructed of different insole materials, including Nora Lunalastik EVA, Nora Lunalight A fresh, Pe-Lite, and PORON Medical 4708 with Langer Biomechanics longitudinal PPT arch pads on offloading plantar pressure on the foot of the elderly with Type 1 or 2 diabetes during gait. Twenty-two elderly with Type 1 or 2 diabetes participated in the study. Their plantar pressure was measured by using an insole measurement system, while the participants walked 10 m in their bare feet or used each experimental insole in random order. The plantar surface was divided into four specific regions including the toes, forefoot, midfoot, and rearfoot. The mean peak pressure (MPP) and pressure–time integral (PTI) of ten steps with or without wearing one of the four insoles were analyzed on the dominant foot and the four specific plantar regions. After completion of the activities, the participants scored each insole from 1 (the least comfortable) to 10 (the most comfortable). The analysis of variance (ANOVA) factor of the insoles had significant effects on the MPP (P < 0.001) and PTI (P = 0.004) in the dominant foot during gait. Pairwise comparison results showed that the MPP and PTI in the dominant foot were significantly lower (P < 0.001) with PORON Medical 4708 than barefoot, Nora Lunalight A fresh, and Pe-Lite. Additionally, the insole materials had a significant effect for the forefoot (P < 0.001) and rearfoot (P < 0.001) in terms of the MPP and PTI compared with the barefoot condition during gait. Regardless of the plantar region, the MPP and PTI values were the lowest when PORON Medical 4708 was used as the insole material among four insole materials. Meanwhile, a significantly lower MPP and PTI can be found in the forefoot and rearfoot with the use of the four experimental insoles when compared with barefoot. The soft insole materials (i.e., PORON medical 4708 and Nora Lunalastik EVA) had a better performance than the rigid insole materials (i.e., Nora Lunalight A fresh, and Pe-Lite) on plantar pressure offloading for diabetic elderly.