Fillers & Additives

Fillers used with various resins give varying characteristics such as minimising shrinkage, reducing weight for a given volume, reducing cost and changing resin consistency.

None of these fillers have a particular ratio; you add to taste or add what you require to get the job done.  Cocktails are very much the order of the day. For instance, you may start with an epoxy resin/hardener base, add some Q Cells Micro to bulk out the mixture, some Mill Fibre to enhance strength and Cabosil to stop the mixture drooping. The result? A Filler Cocktail!

West System® Brand 413 Microfibre Blendis a high density filler used as a thickening agent with West System® brand epoxy to create a multipurpose adhesive, especially for wood bonding.

West System® Brand 410 Microlightis ideal as a low density filler to create a light, easily worked fairing compound with West System® Brand epoxy.

West System® Brand 411 Microsphere Blendis a low density filler used to thicken West System® Brand epoxy for light weight putties with excellent filleting characteristics.

West System® Brand 417 Phenolic Microballoonsis a low density filler used as a thickening agent with epoxy fairing systems to make fairing putties that are easy to sand or carve. 417 Microballoons have a reasonably strong strength to weight ratio, and are recommended as the preferred filler under dark coloured surfaces.

423 Graphite Powdercan be mixed with West System® brand epoxy to produce a low friction coating with increased scuff resistance and durability.

421 Fire Retardant is a hydrated alumina powder that forms a fire retardant mixture when mixed with West System® brand epoxy for coating in engine room or gallery areas.

422 Barrier Coat is a proprietary blend designed to improve the cured epoxy’s moisture exclusion effectiveness, it helps prevent gelcoat blistering and increases the epoxy’s abrasion resistance when mixed with West System® brand epoxy.

Talc – The oldest filler in common use “ it is easy to use, very cheap as well as being very good in compression, but also very heavy.

Q Cells – One of the original micro spheres, bubbles or balloons. It has reasonable compression strength and is generally used to get bulk without adding too much weight. It also sands easily.

Milled Fibre – A fine glass fibre powder.  As with all glass fibre, it adds great strength both tensile and compressive.  Used in a small percentage.  It can promote adhesion to foam cores.

Cotton Fibre – Sometimes called flox or cotton flox or cotton linters.  As with the glass, cotton powder adds tensile and compressive strength. It tends to be lumpier than glass powder.

Chopped Glass – Fibreglass Roving cut into 5 to 8mm lengths.  Adds strength to castings, helps compressive strength, but is quite hard to mix in.

Iron Powder – A very heavy filler.  It gives good wear and abrasion resistance.  Also gives good heat transfer and will give a rusty surface when iron is exposed.  Good for arty products.

Copper Powder – Used for decorative castings and coatings.

Brass Powder – Used for decorative castings and coatings.

Bronze Powder – Used for decorative castings and coatings.

Fumed Silica – Sometimes referred to as Thixo or by its trade name “CABOSIL”.  Fumed Silica is a thixotropic material.  While all of the above fillers increase the viscosity of resin, and if taken to a point of No Flow, will become a very solid mass, Cabosil can be added to get a consistency of Vaseline “quite stiff, but still able to flow”.


  • WestSystem
  • Smooth-On
  • Erapol
  • Environmental Technology Inc.
  • Colan Australia
  • ATL Composites