Resins can be thickened by adding fillers like milled carbon fibre, cutted carbon fibre, microballons or cotton fibre flakes. Thus the resin shrinkage is reduced and strength and stiffness are increased compared to the pure resin.

Milled carbon fibres are used as fillings for thermoplastic and thermosetting resins to increase strength and stiffness or to increase conductivity. The fibres are usually between 0.1- 0.35mm long with a broad scatter in fibre length.

Cutted carbon fibres are available in lengths from 1 to 6 mm.

Microballons are very fine white hollow glass globules. Microballons feature a very low specific gravity. Pastes that are easy to smooth and grind can be achieved with microballons. The compressive strength is increased compared to the pure resin.

Cotton fibre flakes are used in combination with epoxy resin for structural bondings. These thickened resins are light and thixotropic fillers which are also used as coupling layer in mould construction.