I have a foam sandwich racing rowing boat to build starting very shortly. there are some areas that are highly loaded & i was going to incorporate a fiber reinforced foam in the areas where fasteners & stiffening members are to go. This is to link the inner & outer skins better and provide places where fittings can be installed, i dont want to use wood inserts due to risk of expansion if it gets wet.
I will almost certainly  be using a PVC foam  for the main panels but fiber reinforced foam is harder to source.
Airex have just the stuff in their catalogue (Airex PXc / PXw & it would be ideal, trouble is though i can have small samples they do not supply it in the UK.
Anyone know of a source of equivalent core material here in the UK?

these guys have birch,balsa and foam sandwich CF.
Dragon Plate
aluminium honeycomb is out there pre made with CF and by itself to make your own.
you can probably source your own nomex honeycomb and make your own. not sure of cost vs brain damage
 that will work for you.
i ll see if i can find some other sources.

CarbonFiberCreations

searching but so far slim pickings. i ll try and find something in Europe for ya.

CF sandwich

on clearance arimd honeycomb

CarbonFiberCreations

Thanks for the links, interesting stuff. Because of the curves of the hull a flexible insert is required, it seems the Airex ones are extensively used in the windfarm industry in blades. So far a complete blank in the UK, It looks like i am going to have to resort to laminated wooden inserts or lace the skins with roving, an old technique we used to use on bulkheads in the days before vinylester & epoxy! jeez showing me age now!