This article is my opinions and comparisons of the two most commonly used board construction types on the market. Since I work with both types and see advantages of both, I have tried my best to give a non biased evaluation.
True durability and longevity
I think that if you were to ask me today which type of construction would last longer if one were to take care of their board, I would be really undecided. I lean toward polyurethane/polyester because of the fact that I do repairs on all types of boards and some of the poly boards are older than I am (but are not regularly surfed) and they are still functional. Caution though, this is a skewed comparison due to that fact that hand lay up EPS/epoxy construction has not been a widely adopted method of board construction until more recently—thus making the amount of older EPS/epoxy boards much fewer.
Strength of resin properties
Epoxy resin is "stronger" than polyester resin if compared using the same glassing schedule.
Flex
Epoxy has more elasticity, but EPS is more rigid (with more memory though). Polyester resin is a bit stiffer, but polyurethane foam is more flexible. As far as positive feeling in the water, it is subjective.
Buoyancy
EPS is more buoyant than polyurethane foam. It has more air in the blank—more air more float.
Delamination
Air in the blank means it expands faster, leading to more susceptibility to delamination in EPS boards. But with proper care and no exposure to extreme heat, both board types have pretty durable bonding capabilities.
Both construction types can begin to delam, especially in high impact areas (where your feet or knees regularly make contact with the board). Any water damage will drastically increase the possibility of a localized delamination.
Price
Poly construction is typically cheaper that epoxy, due to easier construction and more reasonably priced material.
Environment
Poly construction is more toxic than EPS/epoxy during the building process. But, considering both types, my opinion on environmental friendliness is undetermined—it's about true durability and longevity. If a board lasts longer, I believe that it is more environmentally friendly.
Performance
This is purely subjective, although there are certain situations that I feel that one board type would excel over another.
Art
Poly construction is far more versatile in its ability to have art incorporated into the board—airbrush, resin pigment, tints and glossing are all possible with poly construction. There are more limitations to the EPS/epoxy construction when it comes to art in the board.
Gloss and Polish
Only polyester resin will polish out.
Ability to Use Diverse or High-end Cloths
Epoxy will wet out and laminate a more diverse range of cloths.
Yellowing
Epoxy resin will yellow faster than polyester resin, but the polyurethane blank will yellow faster than the EPS blank. All in all, a poly board will stay whiter longer if exposed to the same amount of UV light.
Shape-ability
Polyurethane foam is much easier and enjoyable for hand shaping— in my opinion. What this means to you, I don't know.
Shock Absorption Surfing the Ride
Polyurethane cores will handle choppy or heavy offshore conditions better than a lighter EPS core will. Making a heavier board with the glass job, but still having a light core, is not the same as having a higher density core. Although a board might weigh the same, it will dampen chop differently depending on the core material and density.
Ability to Withstand a Chainsaw Jab by a Cereal Killer
Both are pretty crummy at this.
Weight
EPS/Epoxy construction can be made lighter. Remember lighter is a great advantage in some conditions, but can also be a disadvantage in others. Again, this is very subjective.
Water Absorption
Both cores will absorb water. EPS will get water in between the cells of foam and potentially suck water more aggressively than polyurethane foam will. Polyurethane foam is more isolated to the area of damage and is easier to dry out and repair—if done shortly after the damage took place
Repairs
Poly construction is easier and typically cheaper to repair. Home repairs with epoxy typically end in an unsealed blank due to the need for exact mixing ratios of epoxy resin and prior water absorption. Or, moisture residue in the blank can create pinholes if not sealed at a descending temperature where the air in the board is contracting and not trying to expand out of the blank.
Sandability
Polyester resins is much easier to sand.
Clarity and Aesthetic Appeal
Both resins come out clear. Aesthetically, a polyurethane blank will look more consistent and less pitted than EPS foam.
Bond
Epoxy has "better" bonding capabilities than polyester resin, but as far as surfboard construction goes, a good lamination is a good lamination. A poor one is a poor one. Polyester bonds well to polyurethane foam, but will eat and destroy EPS foam. Epoxy can laminate either type of blanks, but there has been some debate and documented issues with epoxy laminations over polyurethane foam where there had been foam shrinkage or cavities in the board post lamination. Typically heavier density foams are not an issue in this case.
Foam Rot
Both foams will begin to deteriorate with constant contact with salt water.
Board Snapping
Glassing schedules make this a difficult one to say one is better than the other. EPS foam has less flex than polyurethane, but epoxy resin has more flex than polyester resin. If hit just right, any board with any glass schedule will buckle or snap like a little dead twig. In my repairs I see about the same amount of damage in both construction types.
Ability to Handle Heat
Poly construction is far more capable of handling hot climates, but both construction types are susceptible to delamination, brittling, and cracks due to high temperature exposure, cars, truck beds, and baking in the sun. Dark colors are out of the question for EPS/epoxy for this reason.
Pressure Dings
If compared in the same glassing schedule, poly construction will be more likely to get smaller pressure dings around the board. Foot wells will occur on both construction types.
Blunt-force Impact
EPS/ Epoxy is stronger.
Gouges or Sharper Impacts (rocks, car doors, knives from locals)
Avoid these . . . both construction types are pretty helpless when it comes to these.
Poly