How to Firm Up a Soft Mattress

If you try to sleep on a soft or sagging mattress, your spine may not be supported properly. Improper support of your body while sleeping causes pain and even an inability to sleep. If you're not in the market to replace the mattress, or if the mattress is not yours, you can effectively firm it up with one of two methods. What will work for one mattress may not work for another, so be prepared for trial and error.


Use firming techniques on any type of soft mattress.
  1. Measure the length and width of your mattress and write down the dimensions for future reference.

  2. Purchase a 4- by 8-foot sheet of 3/4-inch plywood and cut it to the dimensions of your mattress with a circular saw. Alternatively, give the dimensions to an associate at your local home improvement or hardware store where you bought the plywood and request that he cut it for you.

  3. Slide the sheet of cut plywood underneath the mattress and on top of the box spring to give the mattress more support.

Mattress Pad

  1. Purchase a firm mattress pad that fits the size of your mattress -- twin, full, queen or king.

  2. Unroll the mattress pad from the packaging and place it directly onto the bare mattress.

  3. Place a fitted sheet over the firm mattress pad to hold it in place on the mattress. Make up the rest of the bed.


  • The home improvement or hardware store may assess a fee for cutting the plywood. Ask in advance, so you know what to expect.

About the Author

Based in Texas, Cynthia Measom has been writing various parenting, business and finance and education articles since 2011. Her articles have appeared on websites such as The Bump and Motley Fool. Measom received a Bachelor of Arts in English from the University of Texas at Austin.