Generally, you don't want the insulation to be dense. The denser it is, the better it is at transferring heat. The best insulator is a complete vacuum, with no light transmission. It's hard to maintain a vacuum in these things, so they fill the cavities with foam to encapsulate air and prevent movement of that air (the foam also stiffens the overall structure). Weight is your enemy when it comes to insulation value, but the heavier coolers are generally more robust because they have thicker walls, better hinges, latches, seals, handles, etc. One reason the Ozark 26 is heavy is because it has what appears to be a stainless steel loop handle, adds weight but helps with longevity. The seal around the top of the Ozark 26 is surrounded by a fairly massive amount of rotomolded plastic, adds lots of stiffness and helps maintain a good seal. The tradeoff is additional weight. A lighter cooler will usually have thinner walls, plastic hinges and latches instead of stainless, etc.