Abstract: An improved mattress innerspring unit is provided including cross helicals which extend transversely of the rows of coil springs and lace together adjacent terminal convolutions of the springs in a row and a retention and support strip which overlies the terminal convolutions of the springs in a row of the unit, the retention and support strip and the helicals being crimped together and otherwise secured about the interlaced portions of the coil springs. The cross helicals are prevented from spinning out of the unit and the unit is firmed, particularly in the area close to the retention and support strip. Preferably, retention and support strips are provided along both the top and bottom terminal convolutions of the coil springs of at least one row near each of the two longitudinal edges of the innerspring unit.