This is a small piece of extremely heavy vinyl.  It is very sticky feeling, with a tacky surface, and the stickiness is transfered to your fingers as you handle it.  It is thin but feels like lead.  I suppose this is what it takes to deaden sound.  It looks like it might melt into a mess in very high heat although I didn't test it for that.  It is described on the box as a "self adhesive, comformable mat that reduces road noise and vibration.The instructions say to:1. Prepare area by removing any carpteing, lining and/or panels to expose metal substrate.2. Clean the surface with rubbing alcohol and let dry.  Ensure surface is free of oil, dust and debris.3. Using standard household scissors cut the 3M Sound Reduction Mat to fit the size of the desired area.4. Peel and discard the yellow liner off the back of the mat.5. Using even pressure, carefully conform and firmly apply to the surface.  If additional conformaity is needed, use a heat gun or blow dryer to heat the mat to 95 degrees to 115 degrees.The box suggests use in the trunk, door panel, or for speaker installations.  My first thought would be the engine compartment but as I said this is something that appears to me it would melt in high heat, and the directions to use a blow dryer to help this conform to curved surfaces supports that viewpoint.  With that in mind, I would be hesitant to use this here in our sub tropic weather where in the summer the interior of a car can climb to well over 120 degrees.  I would be afraid of this melting into a mass of sticky goo.I've seen other sound reduction technologies in cars.  They look more like a thick blanket, rather than heat sensitive vinyl.In addtion, the added weight of several of these in a car is worth considering.  This is like lead as far as weight.In a cold climate this might be ok, but I am going to not use this in our sweltering weather due to the melting propensity of it.If your climate doesn't get extremely hot, this would be OK to place under a speaker or subwoofer installation, as it would help to deaden any vibrations.  If you plan to soundproof your entire car or even just the engine compartment, you would need a lot of these.  This is a pretty small piece when you see it in person.