Saturation Test. EPS vs. PU foam; or Does EPS really suck?

General Discussion
1

There was a discussion on another thread, where I said EPS doesn’t make a good travel  board, because if dinged, it will suck water.  Another sways member mentioned that super fused EPS doesn’t suck water like the regular EPS.  So since I know that other Sways member is doing some pretty interesting  builds, and has my respect, I wondered if I had it wrong.  Maybe the superfused is as good as PU foam.

Well, I had a scrap of Marko super fused blank in my shop, as well as some US Blanks Red foam.  So I did a little test.

I cut two blocks of foam the same size and shape.  Then I weighed them dry.

Dry EPS

Dry PU

The EPS block weighed 5 grams, and the PU block weighed between 6 and 7 grams; the scale kept switching between the two numbers.

I took a jar, filled it with water, and then left teh blocks of foam to soak a couple of hours.

Both soaking.

When taken out, the EPS block weighed 7 grams, and the PU block now weighed 9 grams

Soaked EPS

Soaked PU

So at this point, the EPS isn’t looking so bad.  Both foams added about 2 grams of water.

But then I did something interesting.  I put them both back in the water, and squeezed them.  Just like the board gets squeezed when you stand on it and ride a wave.  When the EPS block was squeezed, lots of little bubbles came out.  That didn’t happen with the PU block.

Soaked and Squeezed EPS

Soaked and Squeezed PU

So after the real world surfing squeeze test, the EPS block now weighed 13 grams, while the PU block grew to 11 grams.

So what’s this mean?  It means that if you ding your EPS board, and stay in the water and surf it, the blank will almost triple in weight, and will draw water through the entire board, as it blows out air when compressed, and sucks water back in when released.  It also means that your PU blank will soak in water locally, but not let the water go in as far.  It didn’t “breath out” air to suck in the same way.  It increased its weight about a half , or 57%

So my conclusion is that for a board that you don’t mind getting out of the water as soon as its dinged, EPS isn’t so bad.  But if you are a long way from home, and you want to keep surfing after a few scrapes, go with PU foam.

 

2

Can’t argue with science. I don’t see the point of using EPS anyway. The stuff is horrible to work with. 

3

Its the difference in external and internal temperatures that waterlogs EPS. …simply placing EPS in water is not the same…when a ding pierces the glass job on an EPS cored board , internal vacuum draws the water in very quickly…EPS foam as a stand alone material , will not absorb water in the same way… it’s the reason why even a small pinhole will suck in a lot of water continually whenever it’s being ridden.

4

Exactly. On other hand, water don ´t affect eps as pu and drain off easier. But no good to let salt in a board. 

5

Then we are agreed: EPS is the devil’s foam.

6

good eps is crap on some of its attributes… not so crap on other attributes…  

All and all I’d say it is valid, and it has a solid place in the game.

On paper the best foam I know is extruded polystyrene… too bad it is like glassing a wax… resin wont stick… who has come up with a good solution?

7

If weight is a target , EPS is the stuff… various fabrics can produce a light strong skin…but the ultra-light targets are a bit “last year” these days…the CDD blank needs to be revisited to produce the best of both worlds. For shape-ability , nothing beats a crisp new PU blank.

8

Personaly i use eps because i can buy, for 3x less than PU, good quality industrial grad eps bloc made in my country in enviromental hi tech factory by one of world leader. Pu here is imported from us, australia or south africa. I cut rocker and foil accurately with my home made hotwire cutter and i shape most of the board quickly with hotwires tool, all scraps are recycled. So it’s right eps take water but 1.9lb density have nice compression and memory resistance and with a decent epoxy lam ended product is quiet durable for better price.

9

Next time I’m surfing I’ll be careful not to squeeze my boards underwater. 

10

The thing about EPS is that when you ding say the rail,

And you keep surfing,

It’s not so much absorbtion.

When you sit there on your board,

You force it under water.

That causes a vacuum.

Sucks water in very rapidly.

When we had a ding repair service in house,

EPS owners would bring in thier boards for fixing.

They would drain for days.

Puddles worth sometimes.

When pool toys were made from styrofoam (EPS) you would pull them out very heavy.

Couple days in the sun, Wala, nice and light again.

Squeezing or vacuum, they do soak water.

Some worse than others.

Multi sized beads seem to do it less.

11

Then when you repair that EPS board with a little bit of water trapped inside…

12

Oh yeah Mako - the good old air volcano

13

After fixing a ding in a epoxy board made by me, I can assure that once you get a ding and let water in, the board will never be the same. The whole water will never leave the entire foam, that seems to me a pretty nasty side of EPS foam.

14

I’ve seen mold grow under the glass from a non-dry repair job.

Mold only needs two things,

Air and Water.

15

…(lol)…oh yes , it’s the anti-christ ! …hellbent on the destruction of humanity as we know it…it was sent from a solar system millions of light years away from Earth , by evil Darleks , who live to destroy us !..run for your life !

16

Don’t be so quick to write it off Barry…that mould may have the cure for a currently uncurable disease , or be a new drug , with all the highs and none of the lows …God works in mysterious ways.

17

Here’s how it works:  EPS is closed cell foam and PU is open cell.  EPS consists of thin-wall styrene balloons that are blown with CO2 which are put in a mold and then fused together into a shape using heat and pressure.  PU is formed from liquid components in a rigid mold.  When EPS is molded into a shape the beads are tightly packed together but there is considerable air space between them per unit volume (i.e. 1lb/cf has more air than 2 lb).  It’s that intricate web of air spaces that water goes into and never comes out when a board is dinged.  This is also what gives EPS a high insulation rating as the air spaces are additive to the R-factor of the beads alone.  In PU foam, water can enter the open cell network of cavities (like a sponge) but it will run back out or evaporate (if the path is left open).  With EPS the water works it way into that maze of air spaces driven by outside temperature and pressure.  It rarely comes back out or evaporates unless you start drilling holes everywhere.  PU foam does not expand with heat as the cells are open and the whole blank breathes as a unit.  Sealed EPS does expand with heat, both the beads and the airspaces.  This is why some water comes out of dings when left out in the sun and it gets hot.  Unfortunately, those same dings act as vents and prevent the pressure from building high enough to squeeze out enough water, which would delam the board anyhow.  Water in EPS boards isn’t going to come out, so take extra precautions to prevent it from happening in the first place.  This means adequate glass schedule for ding protection, but more importantly laminate over any embeds; finboxes, leash plugs, SUP handles, whatever.  Whenever the board gets hot, the expanding core will try and force any embeds out thus micro-cracking the glass around them.  Fortunately almost all everything today is designed for pre-lam install. 

18

I found that by pressuring slowly dinged board with a pump and use of a dry ventilated hotbox, you can evacuate effectively water from eps.

19

cool test mark, and some good info about vacuum and presurising. but seriously i have never had as drastic things happen with open dings before. 

i have surfed open dings with eps in the past and haven’t noticed a weight different in most of them. the ones i have noticed the weight difference have been things like blowing a whole fin box out.

20

just thinking about kayu’s info above about eps alone not absorbing water, but when in a watertight structure it would. In that case, why not utilise pinholes all over the board to prevent the pressurization happening in the first place?