i am preparing to start using some of gregs resin research epoxy, and i want to use eps too. i was wondering if anyone can pass on their knowledge about the differences in flex characteristics between the 2 kinds of blanks once glassed and how it affects performance in relation to rocker. eg the rocker changes made to a salomon plug, or the difference in curve between a polyester and a eps with the same dimensions. i am aware of the volume differences and weight issues. http://www.feraldave.com/sprays.htm 
Hi ya Dave ! I’m down here in deep dark southern Vicco ! I’ve been playin’ with epoxy and extruded polystyrene foam and PU for a few years now and the biggest problem i find with XPS is it is hard to shape on account of the foam being a bit “rubbery” to sand with silicon carbide sanding screen.The foam sort of tears a bit - it doesn’t have that nice, dry, clean-cutability ya get with PU.It also has a very very tight cell formation that requires really fine finish sanding to get grit scratches out.I’ve only used DOW White Styrofoam and Blue LB grade foams - both about 40-45 kg/m2 density - about the same as good Blue grade Bennet PU blanks.Performance-wise the effect of the foam on rocker was hard to tell because i glassed 'em with full 6 oz. carbon cloth top and bottom which made them very stiff but it didn’t stop breakage.I’ve since moved to lightweight PU Green stringered blanks with S-glass fabric and epoxy resin and have got better strength with amazing flex, and easier sanding (black carbon dust in ya sanding and glassing rooms is a nightmare - and supposedly more dangerous to inhale than asbestos fibers !!).Speak soon ! JK.
thanks john, what im really trying to find out is the affect the foam boyancy and flex has on your rocker curves and outlines… how have you changed them to get the benifits of the new materials and flex patterns? http://www.feraldave.com/sprays.htm 
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dave how ya going im not sure if your the guy i spoke to about 8 or 9 years ago one time when you rang me and quized me way back then about epoxy boards are you feral dave boards??? if not i can shed some light on your problem …unless you stiffen your board some other way eps and epoxy is going to flex more ,to compensate in your shape flatter tails are good coz when your not loading them there nice and fast but when you load up in the bowl or hit the lip real hard in a tight spot a little more rocker will flex in which will help them fit in but the best part is the spring you get out of your turns …if you get your best polyester board and copy it in epoxy with eps it will actually go worse. the performance characteristics of new materials need to be taken into consideration . the factors are energy tranfer mainly the speed at which energy can be transfered energy travels at different speeds through different mediums …for example sound travels at 330 meters per second through air 1500 meters a second through water and 5000 meters per second through steel …so just like a surfer trying to turn his board his energy must travel through the board to the water dont rely on what you already know about board design it will confuse you, stick with your new medium make it surf it after a while you will get a feel for what works in epoxy taking into consideration the different float, flex ,and the rate at which energy can travel through the board, your rockers will be different and your outlines will be different.if you built a house you wouldnt use the same design if made from different materials like concrete or wood or steel all have different features …same for boards .in the past ive had really cedible shapers look at my boards and say they were pigs .yet if my boards were made from conventional materials they woulda been right all there knowledge of board design told them that what they were looking at couldnt work …the difference is that because the boards were made from different materials they had never worked and refined ,they didnt have a proper understanding of the design in relation to the materials used .so go by feel work it surf it and make the changes according to the materials, not popular opinion on board design, i cant give specific advice on what to curves to use because even if you use conventional materials designs will still change according to the type of waves your surfing … im outa here cya regards BERT…
When tested in labratory conditions stringerless EPS boards came out significantly stiffer than standard PU polyester boards with stringers. This could be the effect of heavier glass schedules and the better stiffness of EPS over PU. In most conditions you’ll find our standard 2000 resin on PU to have similar flex characteristics to polyester although your weights will be lighter with the same glass schedule. EPS blanks with heavier glass schedules with 2000 will be a bit stiffer. Bouyancy will be a bit better with EPS therefore a thinner shape may be preferable. 1/8th inch is a standard there. We also have 2020 resin which is more flexible and 2040 (in development) which will have even more. I know this is starting with a lot of variables but this will in time lead to more variety in your product line and better product for your customers.
thanks guys, yep thats me bert. thanks for your input, ive been sitting on the edge for a while wanting to use eps and epoxy but scared of the next learning curve. i want to give my customers good products immediatly… http://www.feraldave.com/sprays.htm 
hey guys hi again …greg i was surprised to read under lab conditions that eps was stiffer than stringered pu ??i think i know why now …ive been using way lighter styrene than what you guys use over there …i was reading on another post that the average was 2 to 2.5 pounds per cubic foot and the guy was asking about heavier stuff …im currently using foam about 3/4 of a pound per foot …i think that explains the extra flex… regards BERT
Yes Bert, we usually use 2#. I have used a lot of 3/4 and 1# over the years and there is a significant difference in stiffness. Given the same weight, EPS is much stiffer than PU but if the EPS is very light, it can be more flexible.