First a little background on what Innegra exactly is for those who don’t already know. Instead of copying and pasting and trying to make myself appear smarter than I really am, I have included some homework links.
http://www.innegratech.com/#!technical/flls0
https://en.wikipedia.org/wiki/Innegra_S
https://en.wikipedia.org/wiki/Polypropylene
The first thing to understand about Innegra is it works best with Epoxy Resin. It’s a tough fiber. It offers little in stiffness but can take a solid impact. It also, much like Aramids, offers great dampening which comes into play on EPS boards or boards using a lot of Carbon Fiber. Understanding what a fiber does then points to the orientation based on the desired outcome. With Surfboards, we want the Warp direction (nose to tail) to be rigid enough to hold the shape, rocker etc… So the Innegra by itself laid in this direction without any additional materials would leave a very tough but overly flexible board. Although the type of Epoxy used would add some stiffness, just not the desired result. Innegra fabrics have the tendency to be a bit difficult to work with in a hand laid part. The material has memory and from on a roll it will want to curl. As a result it will want to pull away and not stick down when wrapping rails. It also tends to soak up Resin.
So what kind of Innegra fabrics are there?
-Innegra Plain Weaves and Twill Weaves.These use the Innegra Fibers in both the Warp and fill direction.
-Innegra Hybrids such as Plain and Twill Weaves. These would have Innegra fibers running in one direction (either the warp or the fill) and a Fiberglass or Carbon running in the other direction.
-Commingled Yarns which are a Innegra/ Fiberglass , Innegra/ Carbon or Innegra/ Basalt Yarn. These fibers are intermingled at the filament level.
-Spread Tow Unidirectional all Innegra or Hybrids. This is a relatively newer and pretty interesting process. It takes larger fiber bundles in Carbon (usually 12k Fibers) and Innegra and, using a basic explanation, smashes and spreads them out. The result is a very flat thin product. Traditionally with Carbon Fiber, light flat fabrics come from 1k carbon Yarns. But with carbon, the smaller the Yarn the more expensive. As an example a 3k plain weave 42" fabric is in the $20-30 per Yard Range. A 1k at 42" will be upwards of $90 / Yard. A 6k and then again a 12k yarn are cheaper than the 3k and so the logic goes that a nice thin product that is not nearly as expensive as a 1k woven can be achieved using the spread tow method. These fabrics do not contour well. So not good for wrapping rails.
For board building the Hybrid Fabrics are, in my opinion, the best to use. You do have to pay attention and/or ask about the fiber orientation when purchasing. There are Hybrids that have the Innegra in the Warp which are, as pointed out above, not the best for Surfboard construction. You want to have the Innegra in the Fill direction with either a Fiber Glass or a Carbon in the Warp Direction.
The Fiberglass or Carbon Fiber in the Warp direction helps give the board stiffness while the Innegra in the Fill provides the Impact toughness.
You can also use a all Innegra fabric against the foam and then cap with a regular 4oz or 6oz. This increases the toughness by having the Innegra fibers in both directions and maintains the stiffness with the cap layer. This also gives you a sanding buffer. Just like Aramids (Kevlar, Technora) Innegra does not like to be sanded.
We have found the all Innegra Fabrics, over 3oz, can get heavy in the hand layup scenario. So we have really narrowed our offerings down to a 2oz all Innegra fabric. There are also Vector Net Innegra products which take advantage of the off axis orientation and can offer some laminate support under load like the other Vector Net products (That Chinese finger trap again). Although this does offer the support, it will not be as good as the Technora version. Innegra has much greater elongation (will stretch more) than Technora. I did not originally believe the Vector Net versions offered much in regards to impact resistance due to the gapping of the Yarns. But I have had several customer testimonials swearing it does. The Innegra Fibers are absorbing impact /shock and spreading them along the fibers.
The Innegra/ Glass Fiber Hybrids have been slow to catch on in surfboard construction. I think mostly due to the added difficulty and care needed to properly laminate them. They seem to drink Epoxy and as a result add weight. But a careful lamination can result in a nice light board. A good method for hand laminating these fabrics is to wet the shaped blank first, pull the fabric over and then cut your laps while the Epoxy soaks up through it. You get a much better controlled result and won’t keep dumping resin on thinking you have not wet the fabric enough.
The proper use of Innegra and Innegra Hybrids can definitely help make a better tougher board which lasts longer.
This first pic below is a Carbon / Innegra Hybrid woven as a Hex Weave. It’s basically a modified Twill weave which has Carbon fiber in the Warp and Innegra in the Fill. The other two pics are of our MaxPly product which is a Spread Tow Innegra / Carbon Hybrid. Very thin and light. 40 grams of Carbon and 40 grams of Innegra per side yielding a 80 gsm weight.
