Isolmant UnderSpecial

Isolmant UnderSpecial

Isolmant UnderSpecial

Isolmant UnderSpecial

High performance resilient layer made of 5 or 10 mm polyethylene Isolmant Special joined on the underside to FIBTEC XF1 (special needle-worked fibre produced according to specifications designed to provide a better noise reduction).

It provides excellent impact sound and airborne insulation for horizontal partitions.


8 mm and 13 mm thickness available.



Isolmant Underspecial is specific for floating screeds as provided by UNI 11516:2013 standards with any type of flooring.


Specific for horizontal structures with finishing screed at least 5 cm thick.



Immagine 1


• Excellent acoustic impact sound and airborne insulation.

• Suitable for use in both renovation and new construction.

• Low thermal conductivity.

• Inalterable over time.

• Unlimited durability.

• Contact with water does not compromise performance or characteristics.

• Resistant to mould or insects.

• Easy to lay products.

• Product with overlaps.

• Easy to trim: can be easily cut with a utility knife or box cutter.

Isolmant GreenPlanet

  • • Volatile substances free(VOC A+ | Eurofins Indoor Air Comfort GOLD® Certification).

  • • Eco-friendly and recyclable.

  • • Manufactured with low environmental impact.

  • • Contributes to achieving credits for the environmental certification of a building according to the LEED or ITACA protocols.

  • • This product can be disposed of according to CER n. 170604.

  • • Complies with the requirements defined by the Italian CAM Edilizia for acoustic and thermal insulation materials regarding the request for high acoustic insulation performance, the percentage of recycled material and the absence of hazardous substances.

UnderSpecial becomes Gold

Indoor Air Confort Gold®

UnderSpecial earns l'Indoor Air Confort Gold® di Eurofins


The Eurofins Indoor Air Comfort certification represents the best guarantee at European level regarding the fulfillment of the low VOC emission requirements required by the market.

The standard level "Indoor Air Comfort" shows the compliance of the emissions of the product with the criteria of all legal specifications issued by the authorities of the European Union and its member states.


The higher level "Indoor Air Comfort Gold" ensures further compliance of product emissions with the criteria of many of the voluntary specifications issued by the most relevant eco-labels, with the specifications in the EU and with the requirements for sustainable building certifications (LEED, BREEAM , etc.).


Indoor Air Comfort certified products demonstrate the lowest emissions in the category and are considered the best products to ensure indoor air quality.

Indoor Air Confort Gold®

Item Specifications

Resilient layer is made of reticulated expanded closed-cell polyethylene, with the upper side embossed and screen-printed joined on the under side with a special needleworked fibre that is conceived to enhance the acoustic performance (Isolmant UnderSpecial). To be installed with the Isolamant screen-printed side facing upwards. Product with overlaps.

8 or 13 mm nominal thickness.

Dynamic stiffness 11 MN/m3 or 9 MN/m3 for versions 8 or 13 mm respectively.

Item Specifications Copy item specification

Info & curiosity

slide 1
Particularly suitable for laying under the finishing screed of the flooring (double-layer solution), it requires the creation of a finishing screed with a minimum thickness of 4.5 cm (for UnderSpecial 8 mm) or at least 7 cm (for UnderSpecial 13 mm).
slide 2
One of the historical products of Isolmant's under-screed range, in 2017 on the occasion of the 20 years of presence on the building market, the celebratory version "Isolmant UnderSpecial 20 Anniversary" was created, which lasted a few months and immediately became iconic.
slide 3
Isolmant UnderSpecial, the first coupled product of the Isolmant range, made the history of under-screed acoustic insulation, ending up in the homes of many Italians. But that's not all: it is one of the Isolmant products with the largest foreign market.

Installation information

1/2 - Installation of Isolmant UnderSpecial

Before installing the underlay, a levelling screed must be laid using suitable materials and recipes to ensure adequate mechanical support and a plain and uneven surface.


Then the sheets of Isolmant Underspecial can be laid, which must be carefully joined using the special overlapping fabric and sealed with Isolmant Nastro Telato or Isolmant Fascia Nastro. It is also necessary to be careful to start flush with the wall with the polyethylene, avoiding leaving strips of fibre only visible near the walls: the fibre, in fact, absorbs the cement and stiffens, generating a dangerous and continuous acoustic bridge. It is therefore necessary to trim only the fibre flush with the wall in order to guarantee the presence of both layers of product over the entire surface of the floor.

1/2 - Installation of Isolmant UnderSpecial
Product with overlaps for easy installation.

2/2 - Installation of Fascia Perimetrale:

To avoid acoustic bridges, the use of Isolmant Fascia Perimetrale is recommended, to be laid along the entire perimeter of the room without interruption. The height of Isolmant Fascia Perimetrale must be chosen by the designer/ contractor, taking into account the actual height at each site, in order to guarantee that the band is about 2/3 cm higher than the flooring level.


This excess must be trimmed after laying the floor. The continuity of the installation must also be ensured along the thresholds of entrance doors and French windows, as well as in technical niches for housing the manifolds of the heating system, pillars, pilasters, doors and other wall movements.

2/2 - Installation of Fascia Perimetrale:
The excess of the flanking strip must be trimmed only after the flooring has been laid and grouted.