When using this style of wedge for sitting you may want to consider a higher density and firmer foam, than a back or headrest.

Keep in mind that if you are sitting on it, it will be supporting your entire body weight, you may want to consider a 2 lb foam grade or higher.  The heavier you are the higher the density should be. 

If you are sleeping on it or using it as a backrest you can go lower in density.

A 1.5 or 1.8 lb foam grade is a good option. 

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