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Published on 12 January 2020 15:18

Underlay: Understanding the Manufacturing Methods, Performance and Environmental Credentials of Different Types of Underlay

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Key Learning outcomes
  • Types of Underlay
  • Manufacturing Methods
  • Raw Materials
  • Insulation Properties
  • Acoustic Properties
  • Environmental Credentials
This CPD article aims to provide an overview to the various types of carpet underlay available on the market today. The article aims to inform the reader as to their construction, attributes and manufacturing methodology to assist in the specification and future use of such materials in construction and refurbishment projects.

Carpet underlay performs numerous functions and different products can offer varying attributes which may lead to their specification in certain environments. For example, an underlay with strong acoustic attenuation properties could have poor thermal conductivity, rendering it good for multi-level communal living but poor for underfloor heating.
All underlays however are used to enhance comfort and performance of the environment in which they are being used and ultimately to prolong the life of the carpet under which they are fitted.

Underlays can be tested to several flammability standards including BS 4790 and EN13501. Although not a statutory requirement, commercial textile flooring installations using underlay should specify products that comply with BS5808 and the performance requirements of the Heavy Contract classification.

This article will follow a format for the underlay types which discusses
- Raw materials
- Manufacturing methods
- Insulation Properties
- Acoustic properties
- Environmental credentials
- Applications

1.0 Needle Felt Underlay

This traditional underlay can be made from a blend of recycled fibres – wool, jute and synthetics for example. Felt has a dense structure with excellent resilience and is still widely used in the contract market, particularly in leisure sectors because of its long-term wear resilience making it a very popular choice among contractors when stretch fitting woven carpets.

Felt will typically be a blend of recycled natural and synthetic natural fibres. Once the fibres are blended they are formed into a carded web of fibre of specified weight and then consolidated to final thickness through a needling process.

The needling process ultimately determines density. Thousands of barbed needles catch loose fibres and mechanically entangle them. Density can be controlled by the number of needle punches per square cm and the degree of penetration of the needles. This can be controlled by:
- Needle loom cadence. If loom speed is increased then punches per sq. cm increase, therefore a denser product.
- Production speed. In line speed is increased then punches per sq. cm drops (if needling remains constant) and vice versa.
- Penetration of needles. Needles in the felt sector will typically have 9 barbs on each needle. It is possible to control how many of these barbs are used on a given product. If more barbs are engaged, a denser product is achieved.

The use of a blend of natural and synthetic fibres, and the density of the product means that felt underlays typically conform to the flame retardancy standards without the use of chemical based inhibitors

They are amongst the heaviest products on the market which places them at a disadvantage when comparing them to products like PU or thermally bonded PET based products

Because of the manufacturing process, felt underlays typically have the lowest embedded energy of all the underlay types. This combined with their blended raw materials allows for a product which also has very low VOC content and typically free from formaldehyde.
Needle Felt Underlay
Needle Felt Underlay
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