PRODUCT INFO Medium Density foam has a compression rate of 36lbs. It features the perfect amount of cushioning and stiffness. Its soft but still holds its firmness and support for an individual to sit on it without compressing the foam too much. Medium Firm Quality Foam is designed for heavy traffic and high use applications. 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.