Filler types and applications

Fillers are additives that modify certain properties of resins, for example, hardness and abrasion resistance, chemical, mechanical, thermal, and electrical values. The crosslinking of the binder (resin) should not be hindered by the addition of fillers. Therefore, special care should be taken to ensure that the additives do not contain moisture. This applies above all too natural products such as wood flour or cotton flakes.
Fillers differ in their composition, structure and density.

Organic and inorganic fillers
...are, for example, the natural fibers cotton, jute, hemp and sisal. Frequently used inorganic products are glass fibers, hollow glass spheres (glass bubbles) or metal powders.
In addition to the specific filler strengths, the structure of the fillers determines the properties of the molded materials.

Fibrous fillers
... are, for example, glass fiber chips and cotton flakes.
They improve the tensile, compressive and flexural strength and the fracture behavior. The weight of the filled resin compounds is increased, the flowability is reduced.

Powder fillers
... are, for example, quartz powder, talc and chalk.
Depending on their hardness, they produce very abrasion and wear-resistant resin compounds (quartz flour) or easily grindable end products (talc, chalk).

Spherical fillers
... such as glass bubbles increase impact strength and compressive strength, but not tensile strength.
Due to the ball-bearing effect, they improve the flowability of the resins when added in small quantities.

Thixotropic agents
... are required for thickening resins. They are highly dispersed silicas with a high specific surface area.
Virtually all topcoat resins (gel coat) based on epoxy and polyester resins contain thixotropic agents to prevent run-off on vertical and inclined surfaces.

Colour pigments
Colours are also fillers. Mixing them in is very easy since ready-made pigment pastes are usually available.
The self-rubbing of dry pigments, which is often of poorer quality, is no longer necessary.


Topcoat resins (gelcoats)
Thixotropic agents and possibly color paste

Mould resins
Thixotropic agent and color paste, depending on the desired hardness and thermal conductivity titanium dioxide, quartz powder, steel and aluminum powder.

Fibre filler
glass fibers with a thixotropic agent

Fine filler
A thixotropic agent with chalk/talcum powder

Light putty
Micro-balloons and thixotropic agent

Metal filler
A thixotropic agent with metal powder, mostly aluminum

Coupling layers in mold making
Glass fibre chips with cotton flakes (1:1)

Thixotropic agent, for thicker adhesive joints cotton flocks

Pourable moulding compounds
Cotton flocks

Thermally conductive casting compounds
Thixotropic agents and aluminum powder

Syntactic foams
Light, hollow fillers such as micro hollow spheres (glass bubbles)


Filler / Addition quantity

Recommended addition quantity to 100 g epoxy resin mixture (Epoxy Resin L + Hardener L) for a porridge-like consistency of the mixture.


 Addition quantity (g)/
100 g epoxy resin mixture
(Epoxy Resin L + Hardener L)

 Chopped glass fibre strands 3 mm   65
 Milled glass fibre 0,2 mm  80
 Chopped carbon fibre strands 3 mm  22
 Carbon fibre milled 0,2 mm   25
 Carbon fibre milled extra fine 0,1 mm 37
 Cotton flocks  21
 Thixotropic agent (also TM 100)  7
 3M Scotchlite™ Glass Bubbles 0,12 g/cm³   20
 Micro-Ballons® 0,19 g/cm³ 35
 Glass microspheres 2,5 g/cm³  400
 Talcum (Magnesium silicate) 120
 Aluminium powder 180
 Flame retardant (Aluminium hydroxide) 25
 Silicia sand 400