The "5 Inch Gel Memory Foam Mattress Medium Firm Mattresses CertiPUR-US Certified Bed-in-a-Box Pressure Relieving King Size,Fiberglass Free, White" arrived promptly and was just as described online.As of 12/1/24 there are 1,364 customers who have rated this mattress as overwhelmingly EXCELLENT! I agree that it is:High-quality, 3-layer foam with excellent materials and construction, medium-firm and comfortable, gives an excellent night’s sleep, is easy to assemble or custom-size (see below) and is an excellent value for the money!My review is especially important if you are choosing this mattress to fit onto a custom-sized RV bed!!PROBLEM:  Replacing a custom RV mattress.Hubby and I needed to replace the worn-out Queen+ mattress in the master cabin of our RV.  We chose this excellent KING-sized 5" thick mattress as a replacement, with necessary DIY alterations. Our current custom-fit RV mattress is much larger than a Queen but smaller than a King.SOLUTION:  We ordered the KING 5" mattress, with a plan to cut it down to size in the same dimensions as our old mattress.  The tools required to do this job are a tape measure, marker, long straight edge or yardstick, pair of large and sharp scissors, safety pins, needle and strong (upholstery or button-hole) thread and an electric knife that will be used to cut the 5" thick foam.Step 1: Measure the old mattress and record its length and width. If it is an odd shape, make a cardboard or paper template from the old mattress.Step 2: Open and air out the new mattress for a few days to allow for full expansion and removal of manufacturing odors. Continue airing out until the foam measures a full 5" in thickness.  We accomplished this in our garage on top of two clean, side-by-side, folding tables covered with a clean sheet.  We allowed 4 days for expansion and deodorization in cool, fall temperatures.Step 3: Open the Quilted cover neatly on the side(s) that requires cutting and fully remove it.  Step 4: Now the mattress can be marked for size, by drawing a series of dots about 12" apart along the side to be cut. Use the tape measure and marker to place dots at several locations along the proposed cut-off edge(s).  Step 5:  Draw a long and straight cutting line to connect the dots with the aid of marker and straight edge.  We needed to remove 12" from one side of the foam and 2" from the end.  Mark one side at a time. If the mattress fits against a wall, plan to orient the  mattress to place the cut edge alongside the wall.Step 6:  Use the electric knife to cut a steady, straight and smooth line through the entire thickness of foam in the marked area. If possible, practice cutting a straight line in the piece of foam from the old foam mattress, pillow or other source.Step 7: After cutting, trial fit the mattress in place and make any needed adjustments.  Replace the Quilted mattress cover (a two-person task) and use the safety pins to secure the folded cover over the areas where the foam has been removed.Step 8: Hand-stitch the quilted cover closed over the foam with the needle and strong upholstery thread.Step 9:  Place the new mattress on the bed and check for fit.  Too big?...start over and trim excess foam.SUMMARY:This excellent, medium firm 5" mattress will give you the best night's sleep ever.  You'll wake up energetic and fully refreshed.  The mattress is an excellent value at $110.  We received an estimate of $680 from a fabric store on a 5" slab of foam - no cover or padding.  We saved $570 by DIY with the purchase of this oversized mattress from Amazon!Enjoy!Highly Recommended.