XTR Constructions Custom Flex & Tips

Tools To Order


If you don’t know your volume, it’s because you are getting boards from a garage guy without a shaping machine,or you haven’t got a new board in a while.

Defenition: Volume Is the amount of water displaced by an object. We know that the definition doesn’t help us at all. There are charts that use experience, age how often do you surf, etc.still its very, confusing, and remember 0.5 Lt. can ruin your surfing performance.

Recommendation: for first timers in volume, ask a shaper or an experienced sales guy that can guide you in the correct volume for you.

Once you get a board that you like you need to remember your volume, it’s the best tool for performance surfing.

Calculate your volume: XTR has introduce a Volume calculator for most top new models, Al Merrick also has a volume calculator. Play with different dimensions with this formula, if you don’t see it, call us toll free 855 798 5077 or email at: xtrsales@epoxysurfboards.com


Tips on custom boards and Volume. (assuming you know your volume).


    Having one “all around board” can help your budget, however will limit your surfing tremendously. Even two boards can be a good quiver to start. Think about the waves that you want to shine and focus on that, get the exact flex for those waves using the following tools.

    1. Different constructions.

      If you go from a standard Poly board to a new board that is lighter construction, like, XTR, Firewire or EPS. The rule is to drop your volume up to 2 Lts. If you are a good surfer, and 1 Lt. if you are intermediate surfer.

    2. Smaller Summer Boards.

      You can drop the size of your board and keep the same volume, however if you want a groveler for summer you may want to increase up to 2 or 3 Lts. Allowing you to paddle more on the very small days.

    3. Step Ups.

      When ordering a bigger board, we are thinking on stability, paddle power and durability.
      If you add 2” to 4” in length, don’t be afraid to add 2 Lts.
      If you add 4” to 6” in Length, you can add 2 to 4 Lts. or more, remember the longer the board, the more weight we add so its necessary to add more volume.

    Many customers order new dimensions because they want to achieve either more paddle power or they want to surf a different wave. Here is some tools.


    1. Length:

      Adding 1” to 3” to a surfboard on the same model will increase the rail surface that interacts with the wave resulting in more stability, not always in more paddle power, because when you add length you have to increase the nose rocker. (push more water), its recommended that when you add length you should add some thickness, especially when thinking on a step up. Adding volume when you increase length doesn’t always translate to more paddle power, shorter boards are more maneuverable, even 1” or ½” can make a difference since the whole outline will change, and you have less swing weight, up front.

    2. Width:

      Adding width helps in slow waves and in beach breaks where you get a quick start and to avoid closing sections.
      It’s important to know that if you add width you will increase some volume and paddle power, too much width and you can limit your performance, especially in point breaks going rail to rail. Adding width is good for smaller waves, not so much for step ups (Guns is a different story).

    3. Thickness:

      Adding Thickness will increase volume and paddle power, however thinner boards are more sensitive and easier to control in critical maneuvers, thicker boards tend to go where the water pushes the board.
      Thickness is very important tool to control performance. You can ask yourself, if it’s better to miss a wave or catch a wave even when the board floats too much (extra thick) and you can’t perform, up to you.


    1. Avoid thicker boards, instead go to lighter materials that float more to increase paddle power and performance.
    2. Ask about Concave Deck (CD), with Concave Deck you can reduce the thickness up to 3/8” and KEEP the same volume, you will lower the center of gravity, and increase sensitivity and control,rails will not change.
    3. Get a custom flex, the proper flex can override dimensions.(See chart below for your weight, and wave size).
  • Fins

    There are many options and many combinations, here a few tips.

    1. Never save money on fins, lighter composite fins and fiberglass fins can generate more drive and speed than any plastic stock fins. Having a very good board and bad fins is like a Ferrari with a Geo Metro tires. Removable fins can last many more years than your surfboard. It’s the best money spent after your board.
    2. 3 or 5 fins? if you think that having all options in one board similar than one all around board, you are limiting your surfing too much. Quads can help initiate a turn and work better on smaller softer waves, 5 fin set up will add tail weight and stiffness on the tail on thin boards, and most important you are always wondering if you should switch to a quad or a thruster, surfing is very mental and having to many options can be very confusing for some surfers.


    Have 5 fin option for your small wave board, long fast barreling waves,and your big wave gun,where quads are great, in between stay with your 3 fin. Check the WSL experienced surfers, usually ride 3 fins, unless they are surfing Tavarua or Teahupo.
    If you are intermediate or beginner experiment with 5 fin combos until you decide on your next board.

    • Twin Fins are coming back and some shapers offer a twin Fin with 2 boxes or glass on, that is a proper twin Fin, and can be part of your quiver.
  • Flex

    The Surfboard industry is still doing ok with 65-year-old technology (Polyurethane foam with wood stringer, polyester resin andfiberglass), the main reason is because during the Clark Foam era until 2005, nobody was allowed to have something new (in the USA), we can define our industry Before Clark (BC.) or After Clark (AC.)

    Can you imagine your bike,tennis racket or your skateboard with the technology that is 65 years old?

    Today AC. many companies are introducing EPS core (most absorb water) and carbon fiber combinations, andthey call their ideas new technology, however they are only new constructions with different names.

    It’s very confusing for anybody to choose the right construction. At Epoxy Pro we started working with Epoxy 30 years ago, and we started with what most companies are trying to do today, carbon combinations with Epoxy, still nobody is really recommending what is best for you as a surfer for a specific spot and experience.

    Without that is like saying everybody can ride the same skateboard or have the same tire pressure for any car size, or for any terrain.

    In 2013, we introduce XTR custom flex, independent than dimensions and volume, custom flex is the most important tool today to achieve your magic board for your quiver Its specific for your weight and wave of preference.



Never limit your surfing performance to a traditional Stringer construction, customize your board with XTR custom Flex, different flex patterns according to your weight and wave size.

XTR SL Stringerless:

XTR 7.0 available without Blue center, has enough memory for surfers under 130 lbs. also recommended for high performance surfing on small boards designed with more volume for any surfer.


XTR SL Stringerless:

WAVE SIZE: small.  or

SURFER WEIGHT: under 130

Glass = 4oz. or 6 oz. / 4+4

XTR SL Stringerless

More forgiving than any other construction similar to other stringerless without any carbon, just blue center high density 2” foam that is 100% consistent compare to any wood stringer. Full performance, and Ideal construction for small to medium size waves or surfers under 155 lbs.      ($35.00)

XTR SL Stringerless

  WAVE SIZE: small to 2ft overhead or

SURFER WEIGHT: 120 to 155 lbs.

Glass = 4oz. / 4+4

XTR SL–CK carbon- KEVLAR ®

The latest construction, that combines the best flex pattern for all wave conditions, This construction is extremely easy to surf ,  this particular flex adapts to any wave condition up to double overhead. Tested all over the world. The blank is XTR 7.0 with a 2” higher density extruded blue foam on the center that is 100% consistent compare to any wood stringer. (Red+Carbon)  ( $85.00 up to 6’4”)

XTR SL–CK carbon- KEVLAR ®

WAVE SIZE: Small to double overhead or
SURFER WEIGHT: 140 lb to 175 lbs.
Glass = 4oz or 6oz.+ CK-red / 4+4 + CK- red

XTR SL–CK carbon- KEVLAR ®

The newest addition of custom flex designed for bigger waves or surfers over 175 lbs.  Ideal for bigger waves or bigger guys, creating a much quicker response on each turn. The blank is XTR 7.0 with a 2” higher density extruded blue foam on the center that is 100% consistent compared to any wood stringer. (yellow+carbon)   ($85.0  up to 6’4”)       

XTR SL–CK carbon- KEVLAR ®

WAVE SIZE: Overhead to triple overhead SURFER WEIGHT: 175 lb to 250 +lbs. 
Glass =
6oz. + CK yellow / 4+5 + CK-yellow.

XTR Fx-2

Similar to fX

, with extra durability, we replaced the 1/16” black stringer with a Vacuum bagged thin aluminum foil stripe to absorb vibration, and we add biaxial glass to compensate flex from the carbon rails, XTR-Fx-2 creates torsion on each turn and capable of surfing each rail separately, generating more drive on each turn. Recommended for small to medium size waves and can be customized for bigger waves. ($195.00 up to 6’4”)


WAVE SIZE: Powerful punchy surf
 Up to head high.



It’s not custom unless it has custom Flex…




Custom XTR Flex Chart

Weight Construction

under 130 lbs.             xtr- sl

130 to 155lbs.            xtr-sl  (blue center)

155 to 175 lbs.            xtr-SL CK- (redkevlar)

175lbs & up                    xtr-SL CK- (YELLOW kevlar)




Flex Value


General definition:

Flex is the ability to adapt on a given moment for a particular matter on a specific task.

Flex in a Surfboard:

Is the ability of the surfboard to adapt to the shape of a wave with a specific surfer on a particular moment.

Measuring Flex:

To measure flex you will need an static surfboard with the weight of a surfer, and on a wave, and it’s a difficult task.

Flex Values:

Since measuring flex is difficult and extreemly important for a custom surfboard, we have created Flex Values.



Flex Value Description XTR Construction Compare to Wave Size Your Weight
1 Almost no flex similar to a big wave gun XTR SL–CK carbon- KEVLAR PU WITH 1/2″ +, OR TRIPLE STRINGER BIG OVER 250
2 Very little flex TIMBERTEK(FW) PU WITH 1/4″ STRINGER
3 Some flex LFT (FW) XTR WITH 1/8 STRINGER 190
4 Medium flex with reinforcement XTR SL–CK carbon- KEVLAR PU WITH 1/8″ STRINGER MEDIUM 185
5 Medium soft flex FST (FW)
6 Decent Flex FUTURE FLEX, FLEX BAR 155
7 Flexible XTR SL Stringerless VARIAL, WITH POLY LAM. SMALL 150
8 Very flexible EPS WITH 1/8″ STRINGER 4 OZ.CARBON WRAP 120
9 One of the most flexible surfboards XTR no stringer WAVE STORM, INT, 110
10 Most flexible surfboard UNDER 100