Fiber-reinforced composites are a relatively small segment in the plastics industry in terms of unit sales or total production volume. Innovative and technically sophisticated solutions for the transport & vehicle manufacturing, construction industry, electrical and electronics industries, as well as sports & leisure testify to the special importance and extraordinary appeal.

The interplay of resin matrix, reinforcing material and processing offer a very wide spectrum to meet technical requirements and design solutions.

Composites / GRP

Fiber-reinforced plastics or composites form a subgroup of composite materials. This modern class of materials makes it possible to manufacture high-strength products with low specific weight.


Hand lay-up is the oldest, simplest and most widely used process for manufacturing glass fiber reinforced plastic components.

Advantages of the process:

  • Relatively low mold costs
  • Large-format and complex components can be produced
  • Particularly suitable for prototypes and small batches


  • Medium-sized and large-area parts
  • Machine covers
  • Boat hulls
  • Vehicle trailers
  • Facade cladding

In contrary to hand lay-up fiber spraying is a semi-automated process. Therefore, a mixing gun is used on which a cutter is mounted that cuts continuous fibers (rovings) into a desired length of between 20 and 60 mm, depending on the application. Together with a hardener, the resin is introduced into the mold via the fiber spray gun. As with the hand laminate, subsequent compaction and deaeration is carried out using a roller and brush.

Advantages of the process:

  • Manufacturing of large-area components
  • Fast and cost-effective production
  • Particularly suitable for higher volumes

The RTM process involves working under pressure, i.e., closed molds must be prepared in advance. A resin-hardener mixture is then injected into the closed mold via one or more resin injection ports, where it cures under heat and pressure. Additionally, to improve the resin flow, vacuum can be applied in the mold.

Advantages of the process:

  • Very good, paintable surfaces on both sides
  • Constant, high laminate quality
  • Precisely defined wall thicknesses
  • Sandwich constructions can be produced
  • Particularly suitable for reproducible series production

In this process, the single-shell mold is first lined with fiber materials. Subsequently, the mold is sealed airtight with a special vacuum film and a vacuum of around 0.8 to 0.6 bar is applied. The liquid resin is now sucked or into this mold or injected additionally.

Advantages of the process:

  • Low molding costs
  • High laminate quality
  • Particularly suitable for prototype production as well as for single piece production and small series campaigns

During the winding process reinforcing fibers are pulled through an impregnation bath with pre-accelerated resin and are then wound onto a positive core.

Advantages of the process:

  • Production of cylindrical, oval, conical, and spherical bodies
  • Partially automated process
  • Precisely adjustable wall thicknesses

As a rule, the casting process is carried out without reinforcing fiber. The activated resin is poured into the mold manually or by machine, where it cures. Fillers are often used in this process as well, which can reduce shrinkage, create optical or color effects, and reduce material costs.

The pultrusion process is used to produce profiles and hence, it is also called the profile drawing process. In this process, a defined number of rovings are soaked in an impregnating bath, then bundled and pulled through a heated die for shaping and curing. Precise temperature control is required to ensure complete curing of the material when leaving the mold.

Pultruded parts are characterized by a relatively high glass content and correspondingly high mechanical stiffnesses.

In this process, the reinforcing materials – mat blanks, fabrics or already preformed mats (preforms) – are inserted dry into the mold. Two-part molds are required.

A predetermined amount of the activated resin is poured over the reinforcing material and the mold is closed immediately. The usually high reactivity of the resin leads to a heating of the mold to 40–70 °C and therefore to a rapid hardening of the component.

Pressing compounds (semi-finished products) made of SMC or BMC are used particularly for the production of high volumes of FRP components for the automotive and electrical industries.

SMC – Sheet Molding Compound – processing of the molding compound by compression molding and curing at temperatures of approx. 150 °C.

BMC – Bulk Molding Compound – introduction of the compound into the mold by injection molding or injection compression molding.

Short cycle times and high levels of automation can be achieved with both processes.

In the centrifugal casting, the cut glass rovings and the activated resin are simultaneously introduced into a rotating cylindrical mold. Through centrifugal casting the rovings are impregnated and are being ideally compressed under the effect of centrifugal forces.

Advantages of the process:

  • Production of pipes, poles, rollers, and tanks
  • Partially automated process
  • Continuous processes possible
  • Good surface properties

Industries / Specialties

Fire protection systems

Fires can have devastating consequences, especially where escape routes are restricted. To meet the highest safety standards, Gremolith AG offers products for the manufacture of laminates, coatings and molding compounds that can be used for rail vehicles, shipbuilding, tunnel tubes, chemical plants, or offshore platforms.

Relevant standards:

DIN EN 13501-1:2019-05

  • Fire classification of construction products and building elements - Part 1: Classification using data from reaction to fire tests

DIN 4102-1:1998-05

  • Fire behaviour of building materials and building components - Part 1: Building materials; concepts, requirements and tests

DIN EN 45545-2:2020-10
(formerly: DIN 5510-2:2009-05)

  • Railway applications - Fire protection on railway vehicles - Part 2: Requirements for fire behavior of materials and components

Sewer rehabilitation

For many years, Gremolith AG has been the specialized supplier of polyester resin systems for the trenchless rehabilitation of sewers by means of "inliners". For this purpose, filled UP resins specifically formulated for this application are mixed with suitable hardener combinations so that they are optimally matched to the processing and curing conditions at the customers' site. Depending on the application, the flexible hoses are impregnated with special resin/hardener systems at the customers' site or on site and then inserted into the sewers, where they are cured with hot water or steam. For small sewers or house connections, Gremolith AG also supplies special systems for cold curing at different ambient temperatures.

This type of trenchless rehabilitation creates a new plastic pipe inside the old sewer that facilitates another 50 years of service life.


Hymer – Premium motorhome "Made in Germany"

HYMER has been the epitome of first-class motorhomes for almost 60 years, and it stands for tradition, service and quality "Made in Germany". Thanks to continuous pioneering work in terms of technology, safety, comfort as well as design, they have become the European market leader in the premium segment. The motorhomes are still manufactured in Bad Waldsee today.

HYMER uses GREMOPAL® polyester resin to produce garage tubs, storage boxes, and tubs for holding gas cylinders. The quality of the polyester resin takes is of highest importance and influences the entire manufacturing process. Only polyester resins from Gremolith AG meet the requirements in terms of processing, achieving the required component stability, and a long-lasting durability.

Vacuum injection method

"Besides the reliable product quality, HYMER appreciates the delivery reliability and services of Gremolith AG."

Hubert Schmid, Strategic Purchasing, HYMER GmbH & Co. KG

Thoma-Boote – Swiss Handmade Quality

The boat building company, founded in 1972 by Walter Thoma, produces between 20 and 30 boats per year. Each boat is comprehensively built in the company's own shipyard in Mühlehorn on Lake Walen and is a unique piece with individual finishing. Thoma boats can be found both on national and international waters and are particularly suitable for recreational pleasure and sport fishing. The hulls are hand-made from high quality polyester resins. Thanks to the double hull principle, most models are unsinkable. Carefully selected engines work economically and guarantee reliable operation according to modern environmental standards.


Gremopal® polyester resins from Gremolith AG are used as base building material for the entire shell of a boat.

Hand lay-up

Andreas Nötzli, with his company a customer of Gremolith for many years, particularly appreciates the very fast delivery speed, the flexibility in building material design (color, requirements), and the high quality of the polyester resin.