DAMTEC® Under Ballast Mats are energy-absorbing resilient elastic mats placed under the ballast layer to increase the lifespan of the ballast and overlying track structure.  Excessive degradation of the ballast can contribute to fouling and settlement, which can lead to an increase in impact loading due to the uneven track surface.  Railroads that regularly utilize under ballast mats have found that when under ballast mats are used, their ballast can last up to twice as long.


Under ballast mats can be used in all types of rail construction, including:

  • Freight Rail
  • Passenger Rail such as:
    • Rapid Transit
    • Heavy Rail
    • Light Rail
    • Regional & Commuter Rail
    • High-Speed Rail


When trains move along the track they generate a significant amount of vibration both from the train cars, and the interaction between the train’s wheels and the track assembly. The vibrations of the train cars and the interaction with the train’s wheels and track assembly are transmitted into the structures beneath the track and are propagated to nearby structures and buildings. Depending on the size of the train, the age of the structure, and the construction of the bridge, these vibrations can cause effects ranging from annoyance to structural damage.

  • Asset Protection: Prolonged exposure to consistent, repeating vibration can enhance both fatigue and resonance effects in the track bridge assembly and will reduce the life of the ballast and damage structural elements of the bridge. By creating a cushion for the base layer of ballast, and absorbing the vibration transmitted through the track assembly, the DAMTEC® Under Ballast Mats can help maintain the shape of the ballast, and extend the life of the bridge structure.
  • Noise Reduction: By reducing the magnitude of vibration transmitted through the bridge structure, and propagated into adjacent structures, the DAMTEC® Under Ballast Mats reduce the noise generated both around the track structure and in adjacent buildings.


Property DAMTEC SBM K 10 Under Ballast Mat DAMTEC SBM K 20 Under Ballast Mat
Thickness 0.4 in (10mm) 0.8 in (20mm)
>Width 4 ft (1,250mm) 4 ft (1,250mm)
Length 20 ft (6,000mm) 13 ft (6,000mm)
Weight 1.3 lbs/ft² (6.5 kg/m²) 2.7 lbs/ft² (13 kg/m²)
Cstat1 0.12 N/mm³ 0.06 N/mm³
Cstat2 < 0.149 N/mm³ < 0.061 N/mm³

Static bedding modulus measured in accordance to DIN 45673-5.


Protects waterproofing membranes from damage

Extends the life of the ballast

Protects adjacent structures by reducing vibrations

Environmentally friendly

Extremely economical

Easy installation

Low water absorption

Extremely durable

Reduces the transmission of structure-borne sound

Reduces the transmission of secondary airborne sound

Maintains the track position for longer periods of time


What are DAMTEC Under Ballast Mats made of?

DAMTEC® Under Ballast Mats consist of a proprietary mixture of polyurethane foam and high-quality, virgin rubber granules with a polyurethane elastomeric bonding agent. This unique, specialty blend, delivers the properties required to reduce vibration, protect the structural elements, and dampen noise while reducing material consumption. These same elastomeric materials are also used in other demanding areas such as building construction, civil engineering, excavations, and tunneling.


With the extensively tested formulations, the products meet specific requirements resulting from the loads in the track area. The unique composite of materials maintains its performance throughout the calculated life-span, which guarantees a consistent, high level of effectiveness over decades and efficiently counteract the multi-frequency vibrations and shocks that are transmitted through the structure.

What does DAMTEC SBM K stand for?

The term is an abbreviation of the following words:

Kautschuk (rubber)

What form are DAMTEC SBM K mats delivered in?

The DAMTEC® Under Ballast Mats is supplied as standard 4 foot (1,250mm) wide roll. Depending on the thickness, different roll lengths are available. Pre-fabricated sheets or other custom lengths can also be produced for certain project requirements.

How are DAMTEC Under Ballast Mats installed?

You can find detailed installation instructions in our download area.  You can also find a short video directly below.

How long has DAMTEC Under Ballast Mat been on the market?

DAMTEC® Under Ballast Mats have been successfully installed for over 20 years.  The first project specifically using the SBM K was the “Viadukt Sembrancher” in Switzerland in 1997.  DAMTEC® Under Ballast Mats have been used throughout Europe, Asia, and Australia, including numerous major projects such as the Wiener Linen, the tram in Graz, the Butler Extension in Perth (Australia), and the metro in Kuala Lumpur (Malaysia) with Under Ballast Mat.

How will the DAMTEC Team support my railway project?

Solution Development & Detailed Solutions
For more unique or complex projects, DAMTEC’S years of experience with acoustic and vibration reduction products are a guarantee for the solution of even very complex problems. Our specialists will develop custom specifications and product recommendations to eliminate or minimize damaging and disruptive vibration. In addition to standard solutions based on experience, we are of course also technically and personally in the position to implement completely new solutions, exactly adapted to your requirements.


Calculations, simulations and efficacy forecasts
With DAMTEC, you don’t need to wait for installation and return to service to determine the effectiveness of your selected. After a preliminary inspection and analysis of the conditions on site, our specialists are able to create a calculation model in which all relevant factors regarding vibration and damping behavior with different material properties are taken into account. We deliver a realistic simulation that allows fine-tuning of these factors and enables our specialists to develop the optimum solution. At the end of the planning phase, you will receive proof of the expected effectiveness of the system. This efficacy forecast gives you assurance in advance that your expectations will be met successfully.


Our services at a glance

  • In-house material testing and measurement
  • Project support from the beginning
  • Installation advice and site support
  • Custom specification and of installation plans
  • In-field vibration and mechanical measurements
  • Project-specific solutions
  • Calculation and simulation
  • Efficacy forecasts
Technical terms - Demystified!

Static bedding modulus

With bedding theory, the track is imagined as an infinitely long rod that is laid on a continuous, elastic base. The bedding modulus is the elasticity value of the whole system, rail – railroad tie – ballast – substructure – substrate, and is used to estimate the static deflection of the operating load. This quantity is a measure of the stiffness that must be determined experimentally. The static bedding modulus basically indicates how deep the rail sinks under slow traffic conditions or a stationary train.
The bedding modulus is the ratio of the stress to the deflection. Usually, the secant modulus is measured, for example, between 0.02 N/mm² and 0.10 N/mm² . Alternatively, the tangent modulus can be determined.




A distinction must be made between the deflection and subsidence of the elastomer and the rail deflection. The deflection can be determined using the spring characteristics and is the distance in millimetres by which the material is compressed under a certain tension.
The rail deflection when in use takes into consideration the stiffness in the track superstructure from the vehicle to the substrate. It is calculated statically for the stationary and dynamically for the moving train. Depending on speed, axle load, superstructure type, sub-type and DAMTEC® type, the deflection is usually between 1 mm and 3 mm.



Dynamic bedding modulus

A distinction must be made between the low-frequency (superstructure dynamics) and the high-frequency dynamic bedding modulus (damping of structure-borne noise). With the first-mentioned characteristic value, the bending deformation of the rail under the rolling wheel can be estimated from the interaction of bending elasticity of rails and railroad ties, including ballast.
The higher-frequency dynamic bedding modulus of a ballast mat influences the natural frequency of the elastically mounted superstructure as a vibratory system as a whole and thus the insertion loss. The test is performed with a static preload.



Insertion loss

The insertion loss ΔLe (in dB) is a characteristic value that expresses the extent to which inserted measures contribute to reducing the structure-borne noise introduced into a system. The insertion loss ΔLe is the ratio of the structure-borne sound power “without installed measures” to “with installed measures”. It is a characteristic value of the entire system – from the vehicle to the substructure.



Forecast calculations

Since the mechanisms for the generation and propagation of structure-borne sound associated with rail transport are widely known, the expected effect of mitigation measures can be calculated in advance after a thorough evaluation of the system in the way they are to be used. There are many tried and tested calculation models available for this purpose. The combination of advanced materials that meet all modern requirements for effective sound and vibration protection, as well as the vast experience in implementing more effective measures make DAMTEC® the ideal partner for sound and vibration reduction in the railway sector.


Document Download Link
DAMTEC Sub Ballast Mat Brochure Download
Sub Ballast Mat Installation Instructions Download
DAMTEC SBM K 10 Data Sheet Download
DAMTEC SBM K 20 Data Sheet Download