We have been experimenting for several years with a variety of materials to develop light and stiff structures.  When you can, with little force, twist your stab relative to the wing, you have to wonder if that is happening when you complete a hard radius in a strong wind, or a snap.  Gray says he's actually seen this in flight.  I can't say I have, but I have bent wing tubes, push rods, and witnessed aerodynamic failures that prove the airplane has a lot of forces on it. 

Stiffness keeps the flying surfaces in alignment and the pilot in complete control.  It eliminates a common variable.  However, we only need so much of this.  Stiffer may be better, but not at the expense of weight.  This is where carbon fiber comes to the rescue (to a point). 

Carbon fiber is stiffer than glass of the same weight.  This was great for us with the old style of pattern planes, but now the huge fuselages have increased the surface area.  To get a plane that can be built under 5 kg (11 lbs) without magical building skills pushed us to use less weight of carbon fiber, composite laminate materials (nomex, foam(s), mats), other cloths (kevlar, glass), different weaves all in various permutations and combinations.  Vacuum bagging and wet layups give different results too.

A laminate uses a core material to hold the inner and outer skins in place.  This 3 dimensional structure is very stiff, therefore light glass cloth can be used for the skins.  If a light core material is used that can stabilize the skins, you can fabricate a material that is lighter than the "old school" practice of using a few layers of 4-6 oz cloth.  Some manufacturers use styrofoam for their core (PL Prod, ZN line, CA models).  This is a poor material because it does not stabilize the skins well.  These planes ding easily and are not very stiff, requiring internal bracing.  Other manufacturers use urethane foam.  This is stiff and brittle so it can crack, and these cracks can migrate.  The loss of many dozens of Impacts from Composite-Arf due to fuselages breaking is evidence of this.  AeroSlave core material is not used by anyone else.  It is harder to manufacture with and the final results may be about 2 oz heavier than styrofoam.  However, it is stiff and tough (can flex without breaking) and lasts the longest.  It will not need internal bracing, so this saves the builder time and weight resulting in a net gain. 

The "final" laminate construction used by AeroSlave wasn't easy to nail down.  We build a bunch of test planes  in different ways until we balanced weight and strength in an optimal way.