The only difference between the 2 is the metal plate underneath that joins the 2 outside rails. Usually used to extend an Isolated section that activates accessories when the trains wheels roll over , like the Lionel Crossing Grade with flashers. Insulated track is used between the accessory and an Isolated track section. One side of the outer rails triggers the accessory, so you don't want the metal plate joining the outside rails or it would not work. You don't want to use that for your regular track or you would have to attach 2 common wires to your track to keep both sides of the outer rails connected to common. The metal plate also helps if you get a loose track connection on one of the outer rails. Because they are joined together, that section would still get its signal from the other side. Isolated Block sections are different and only come in 5" sections. That have all 3 rails split in the middle and underneath have jumper wires you can remove to electrically isolate that rail, like when you want to turn off a whole section of track.
Track on right is the insulated Track, notice the metal plate is not there between the outer rails.
Below is an isolated section, top and bottom.
