Hi SophiaInBoston,
They would have different firmness levels, different foam densities (you would need to check with Dreamfoam for this but I believe it may be 1.5 lbs), different prices, different designs, and different return policies even though they use the same type of material (polyfoam). Dreamfoam also has a 12 in 1 customizable mattress here which would be more comparable in terms of the density of the polyfoam (it uses 2 lb density polyfoam and the Tuft & Needle uses 1.8 - 2 lb density polyfoam) and there is more about the differences between the 12 in 1 customizable and the Tuft & Needle 10" in post #4 here.
Phoenix