The Big Rig Mattress BRM4875E 48 Inches x 75 Inches Extra Firm Mattress This product is engineered with a high performance pocketed spring core that promotes proper spinal alignment and reduced pressure points; The springs in our cores are made from heat treated, high tensile strength spring wire for exceptional durability The zippered cover allows for the removal and replacement of the plush cover in the event of damage The quilted top has a premium quilt pattern and uses the highest quality quilted materials