The 8" stack (the 3" riser on top of the 5" riser) is too unstable when used on a bed. I toss and turn when I sleep. The first night I used the 8" stack to raise my bed, one of the stacks toppled over in the middle of the night. I since have used just the 5" riser, which means not stacking the 3" riser on top of the 5" riser), and it works fine, just as intended. I'm sure the 8" stack would be fine if used on furniture that simply stands there and is not jostled.See full review