Questions about using HD foam inserts in 1 pound EPS

I just read through a ton of threads dating as far back as 10 years ago about installing Futures fin boxes and a Fins Unlimited center boxes into EPS. I want to check and see if what was good then is still recommended – or is there a better way now.

I’m pretty sure I’m going with 1 pound EPS for my next board with no stringer and have these questions, please…

  1. Is it still recommended to use HD foam inserts with 1 pound EPS or is there a better, simpler way now?

  2. Is it still okay to NOT use HD foam inserts when using 1 1/2 pound EPS?

  3. Will I need an HD foam insert around the leash plug too?

  4. Can I buy a small quantity of HD foam cheaply from a local hardware store like Ace or Home Depot? If so, what kind of HD foam should I buy?

  5. After sealing with spackle, I was going to color the shaped blank with acrylic paint and then glass clear. I’m concerned about the difference in color between the HD foam inserts and the surrounding EPS. Should I be concerned about this or does the acrylic paint blend nicely so that the color difference between the two foams is not discernable? Any suggestions?

  6. How much wider, longer, and deeper should the HD foam inserts be compared to the actual sizes of the Fins Unlimited center box and Futures box?




Why not let the inserts show? If done nice they add not subtract from the look. Just like all choices for board construction (glass weight, layers, rail wrap, etc) you chose between weight savings and longevity. The size and shape of your inserts is another choice you make for strength vs. weight. one thing I would advise, the gluing in of the Longboard style finbox reinforcement can change the shape in 1 lb foam, ie. flatten that area, if done after shaping. I reinforce the leash plug myself. But, I don’t think you have to if you use a glass over style plug.


Why not let the HD inserts show? Well, I might have to but I’m concerned about if I mess them up a bit. So the time to do the inserts should be before I start shaping? Any thoughts on the difference in color after painting the sealed EPS with acrylic?

Depending on board size, the difference between using 1# EPS vs 1.5# EPS may only amount to 1/2#, and that’s before consideration of whatever extra fiberglass/resin and finbox reinforcements you use to compensate for the weakness of the lighter foam.  Just one extra layer of fiberglass can add all of that weight back in.  

Unless you’re planning on vacuum bagging on wood skins or some other heroic efforts in your glassing schedule you might actually save a little weight AND get a stronger board by using a slightly heavier core.  

True that !

I get your point about how HD inserts and extra reinforcement here and there probably isn’t worth the hassle. No I won’t be bagging this board and the more I read the more I think I should go with 1.5 pound EPS.