Every material has it’s good and bad points which I will try to cover for each core. Many companies use the same material, but coin different names, so I will not be using the individual names each company uses. Also, some companies have exclusive materials that I have not used , so I cannot offer an opinion on them. In my opinion there is no best material or material combination for everyone since we all have different needs. I hope the following will give you some useful information. 

The combination of materials will determine the flex, flotation, “spring effect”, stiffness,  and over all longevity  of a board. 

Cold water will increase the stiffness and warm water will increase the flexibility of all boards. 

Most boards start as a blank and are then cut and shaped. Heat laminators are used to bond the skins to the core.  In order to create a good bond the skin and core must contain a certain amount of the same polymers. The approximate temperature used to bond the skins to the core is 650 to 850 degrees Fahrenheit.  Since heat effects all foams differently the temperature and speed settings during lamination are adjusted for each core and skin combination to ensure  proper lamination. Too much heat will make extruded foams shrink and beaded foams expand. Rail skins are generally applied using heat guns,  so temperature and speed fluctuate on each board.  Applying and trimming rail skins is the hardest skill to master in making a board.

Other factors that need to be taken into account during lamination are humidity and room temperature.   Manufacturers need to take these factors into account as the seasons change.

Deck skins and bottom skins are generally laminated on different days allowing the core to cool between laminations. 

The density of foams is measured in “pounds” the higher the number the greater the density and strength. 

The two dominate deck skins are cross linked and non cross linked.  Cross linked skins have very small “air” bubbles making for a cleaner finish.  Non- cross linked skins have larger “air” bubbles which increases flotation and cushioning  when landing air maneuvers. 

Hard bottoms  increases stiffness but weigh more and can crack.   Also,  once they crease a hard bottom will tend to hinge and flex  in the same spot breaking  down the core’s cell structure. Soft bottoms are light and allow the board to flex more allowing the rider to manipulate the rocker.  Soft bottoms also, allow the board to flex in different locations reducing core cell damage. 

As a general rule extruded foams will return to their original rocker faster than beaded cores. This gives more projection because as you make a turn the board flexes increasing the rocker.   As you come out of the turn the forces that increased the rocker are decreased and the board can return to it’s original rocker. This creates a sort of “spring effect” adding to the speed gained from a turn. 

Stringers are used to increase stiffness, decrease creasing,  and to help maintain good rocker. Stringers  are generally inserted into the center of the core. Stringers are made of  many different designs and materials.  The main disadvantages of stringers are the loss of the ““spring effect” and the loss of the ability to manipulate rocker such as adding rocker while stalling and bottom turning in hollow  waves.

Stringers also damage the cells allowing for water absorption and the possibility of the stringer ripping through the core and popping out the deck or bottom skin.

Another way of stiffening  a board and increasing the “spring effect” is to laminate a material between the deck and or bottom skins.  Stiffeners can be foam or other materials that  increase stiffness.

All “Polypropylene” cores use intermediate foam between the skins and core to create a good bond.  The intermediate layer also aids in stiffening the board. 

Have a cell structure like a “STYROFOAM” cooler. Small beads are put into a mold and heated until the beads expand to fill the mold. The core is then stored to allow it to cure and let gasses escape. Beaded foams are more expensive then extruded foams due to the cost of raw materials and the time to make each core. The cell structure of beaded foams create a stronger material compared to extruded cores , but when flexed return to their original shape slower then extruded foam. Advantages of beaded cores are stiffness, product  longevity,  water resistance, and less rocker distortion.  Disadvantages are high price, prone to denting , less “spring effect” and less flotation. 

Extruded foam is made in long sheets and is cut to size by the manufacturer.  Extruded foams contain “air” bubble cells.  Chemicals are mixed by large  machines and then forced out an opening mixed with a chemical that infuses the “air” bubbles. The cost to make extrude foam is far less expensive than beaded foam due to the speed of manufacturing and cost of raw materials.

Advantages of extruded cores are lower price, increased flotation, dent resistance, greater “spring effect” and,  cushioning when landing air maneuvers. Disadvantages are less stiffness, rocker distortion, prone to cell damage and water absorption. 

Combination cores are made by laminating two or more different materials together. A combination core can be made using a layer of extruded foam and a layer of beaded foam or the same type of material , but with different densities. 

Extruded “Polyethylene” also known as “DOW CORE”, “PE CORE”,  and other names coined by companies has been the dominate core material since the invention of the Bodyboard. “PE” is  relatively inexpensive and is readily available. But since the EPA changed the laws regarding chemical emissions several years ago the strength of the material has decreased and thus the life of the high performance board, which spawned the development of stiffeners like stringers, intermediate stiffening layers of foam,  and other materials.

“PE” is the core of choice for entry level boards  offering a good price to performance ratio. “PE is also good for cold water conditions, since low  water temperatures increase the stiffness of all cores.

Boards of 40 inches and under are short enough  to remain stiff resulting in good performance for small riders. Since “PE” contains air bubbles it is soft to land on when doing aerial maneuvers. “PE” is very dent resistant but as pressure is constantly applied to the same location the “air” bubbles will break down causing a mushy feel to the area. Water absorption is caused when the cell structure of the “air” bubble is damaged by either constant impact or cuts exposing open cells. 

“Polypropylene” also known as “PP”, “POLYPRO”,  and other names coined by companies is available in beaded and extruded cores. This is creating some confusion in the market . Since the material “polypropylene” will follow the rules explained regarding extruded and beaded cores. The main advantages of  “polypropylene” are memory.  The material has superior retention of it’s original shape. Light weight  “polypropylene”  has an excellent strength to weight ratio and water resistance.  “Polypropylene”  remains  water resistant longer then most cores. A beaded “polypropylene” core will not dent as much as “ARCEL” but will follow the same rules of beaded cores, less “spring effect”, cost, etc.  Extruded “polypropylene” follows the same rules regarding extruded cores, but since it has better memory the “spring effect” is  enhanced. 

“ARCEL” is a beaded core.  “ARCEL” started to show up in the late 80’s as a high performance core material due to is superior strength over “PE. “ARCEL”  will maintain it’s rocker and stiffness giving you about twice the performance life compared to “PE” especially in warm water.

The main draw back of “ARCEL is it will dent  particularly where your elbows contact the deck and where drop knee riders put there knee.  The dents are viewed differently by each rider, some like the indentation at the elbows because it helps to keep there arms from slipping off the board.