High density foam has a compression rate of 35 lbs. Higher density foam will remain responsive longer, it features the perfect amount of cushioning and stiffness. Higher density firm quality foam is designed for heavy traffic and high use applications. (high density) 100% recovery rate fire retardant durability : durable, high density foam suitable for long-term use. Density and compression indicate the softness and longevity of foam. Compression = firmness compression (not density) is what determines firmness. If you don t want a cushion that s hard as a rock or a mattress that sinks when you sit on it, you have to check the compression or ild number. Compression means the number of pounds necessary to compress a piece of foam 25% and still bounce back to the original thickness. For example, a 4" thick piece of foam that requires 35 lbs. To pack it down 1" and have it return to its full 4" thickness has a 35 lb. Compression rating or ild indention load deflection. All foam sheets are sold per sheet not per yard and rolled for packaging. Packing, shipping & cutting foam packages need to be opened immediately once you receive the package. Do not let the foam sit unopened for more than 1 week. Do not open with a box cutter. Use a ball point pen or a pencil. Start by making a little incision and break it from there. Durability : will last 7 to 10 years. Care instructions : when unpacking, allow at least 2 days for the foam to breathe in order to recover its original size and form.