What's in the box?* One sound-deadening sheet approximately 5/32" thick.  You can use it as one mat, 19 11/16" by 19 11/16", or as two smaller mats (it has a perforation down the middle).* Instructions.In general, I find 3M products to be of superior quality.  I do like this product, but have some reservations.  In regard to performance, it DOES work!  I used it for an application other than an automobile, which is also other than its intended purpose.I have a small work/storage room in my basement.  It has slab floor, drywall, and is narrow, less than 5' wide.  I have a backup sump pump in the room, which has a control module which manages the backup pump's battery, etc.  The module has always produced an electrical buzz/hum, which can be quite annoying when in the room.  The module is in the corner of the workroom on a small cabinet, so it is about 5" from a wall on two sides of it.  The walls both have pegboard, and in the past I tried fixing some Styrofoam to board by the module.  This served only to slightly amplify the buzz.So I decided to try this product.  For my application, I mounted some 1/8" thick wood that I had from a packing crate on the pegboard.  I did this, so I would not damage the pegboard with the 3M mats.  The mat gripped well, but like anything else of an adhesive nature, you want to measure right and work slowly, as adjusting it afterward is not really an option.  Once you have peeled the paper and applied it, it is on fairly well.  You could get it off, but would likely wreck it in the process. As far as sizing it, cutting this is like cutting other dense, adhesive type materials.  A sharp blade with firm, steady strokes is best.  The blade will get a little gummy so plan on changing it out or cleaning it afterward.  TIP: If you rub a little WD-40 on sides of the blade, it helps it glide through a little more easily.For my purpose, I separated the mat into two halves at the perforation.  I needed to trim them slightly to fit my application.  I applied them so that the module had a mat behind it and on one side.  I didn't think I'd have great results, especially with two sides still not dampened.  However, the sound of the buzz was dramatically reduced.So, this stuff works, and it adheres well, etc.  Now the issue: there is not a lot of it to a box, and at over $15 a box, it can be pricy per square foot.  If you are using this to deaden sound in a whole car, or even a large area of a car, four doors, trunk, etc., I could see it get expensive very fast.It does work as advertised.  I think there needs to be a little more per box to warrant using it, unless you have a very specific application in a contained area (one door, one speaker area, etc.).