BATSAFE Development: Summary of Testing

TLX BATSAFE has passed the Bat Conservation Trust modified pilling tests.

(Method for evaluating the snagging propensity of roofing membranes in buildings by roosting bats, Building Research and Information, 2020, 48(4), DOI:10.1080/09613218.2020.1763773.) 

tlx batsafe testing


Because of concerns about bats becoming entangled in the polypropylene filaments of modern breathable roofing membranes, the Bat Conservation Trust sponsored a PhD student (Stacey Waring, University of Reading) to research into the problem. The research project was narrow in scope, only considering traditional cold lofts, and, in spite of citing evidence of bat deaths associated with bitumen felt1 (2 out of 16 UK instances) only breather membranes were investigated, even though uric acid (present in bat urine) is known to degrade bitumen felt. Following this work she recommended that only 1F felt be used where bats were present.

Although most of TLX Insulation’s business is with roofs with rafter-level insulation,  (rather than cold roofs) the requirement  for a 50mm ventilated space beneath 1F felt significantly alters the insulation buildup possible (and often limits the U-value achievable), so the development of a breather membrane that would not pose an entanglement risk to bats was considered worthwhile. Dr. Waring was employed as a consultant to carry out testing by TLX Insulation (as part of her postdoctoral research) into how the addition of a mesh might make TLX breather membranes safe for bats by preventing their claws from contacting the membrane. TLX also looked at the impact Bitumen 1F felt could be having, more information is available on our BITUMEN 1F PAGE

In vivo testing of experimental prototypes at the Isle of Wight Bat Hospital.

The aim of this research was to determine an optimal mesh size that would prevent bat claws from ‘fluffing’ out the polypropylene spunbond fibres in which they can become entangled, whilst still enabling the bats to crawl over it and of such a size that bat droppings did not block it.  

Under Dr. Waring’s supervision some trial membranes were tested over several months at the Isle of Wight Bat Hospital, lining sections of the bat aviary both vertically and horizontally. Trial membranes were based on standard TLX UV membranes bonded to mesh of various sizes (23mm, 15mm, 6mm and 4mm square meshes) and monitored daily. The ongoing observations were the subject of 3 reports from Dr. Waring, plus a final removal report in October 2016, stating that the smallest size mesh ‘does a good job of protecting the membrane from the abrasive bat claws’.  Development was therefore directed towards manufacturing a small-mesh product with a reliable and breathable adhesive layer.

The next stage was to adopt the same laboratory methods Dr Waring had used in her research to develop a suitable prototype membrane with mesh bonded to each side.

Choice of mesh, adhesive and process requirements.

Although simple in concept, the development effort to manufacture such a mesh-covered membrane was considerable. A number of meshes were trialled to find the most suitable, and several methods to attach it to the membrane were considered.

Abrasion testing

In order to test the resistance of the trial membranes (with 9 different meshes) to abrasion a standard abrasion test (ISO 105-X12:2016) was used, modified such that Velcro (hooked side) was used as the abrading surface (following Dr. Waring’s findings regarding the suitability of Velcro for simulating the plucking action of bat claws– see below). However it was apparent that in this test shear forces were responsible for the abrasion rather than a ‘plucking’ action of the Velcro hooks, so it only served to rank the meshes tested. 500 strokes of the ‘rubbing finger’ showed differences between different meshes, with the 3mm mesh having superior resistance and protecting the spunbond beneath.

This lightweight 3mm mesh with strand thickness of 790 µm was flexible, and the light weight meant that the product was not too heavy for roofers to handle safely. The adhesive itself took the form of a mesh, enough to bond to the membrane yet with sufficient clear area not to compromise breathability. After the usual process development trials (bonding temperatures and pressures, line speed, etc.) the manufacturing process conditions were established so as to satisfy the standard internal laboratory tests for breather membrane tensile parameters and breathability.

However, confirmation of the composite membrane’s behaviour in relation to long-term exposure to bat claws was required, and so the laboratory test method previously used by Dr. Waring was employed.

Pilling test

  1. BS EN ISO 12941-1:2001 Textiles – Determination of fabric propensity to surface fuzzing and to pilling) to model the plucking action of bat claws on breather membranes which caused them to ‘fluff’. This test involved mounting the test fabric on tubes which were then placed in a rotating cork-lined box, that had been modified by mounting strips of Velcro inside. At the microscopic level, the Velcro hooks closely mimic bat claws. 





The new membrane was tested up to 75000 rotations, inspecting samples at intervals and photographing, and compared with controls of the standard UV 10 breather membrane. Both sides of the membranes were tested.


The basic membrane showed the typical ‘fluffing’ similar to that created by bat claws after relatively few rotations – typically 250.



Dr Waring`s estimated that 3000 rotations of the pilling machine would replicate bat activity for approximately a year. We ran this test for 75,000 cycles ( this represented the 25 year life of a roofing underlay). There was no evidence of fluffing of the non woven layer. 

Fluffing Test:

This test is designed to replicate a bats claws teasing the fibres of the breathable membrane loose and causing fluffing. These fluffed fibres cause bats to become entangled. The test uses Velcro hooks to lightly rotate across the surface of the membrane to replicate a bats claw plucking and pulling the fibres loose. The result of this test accurately replicates what we see in a roof when bats come into contact with a breathable membrane.

The result showed extensive fluffing on a breathable membrane and no fluffing on TLX Batsafe.

Breather membrane tests

Before the product could be UKCA marked as a breather membrane, the standard industry tests for waterproofness, tensile testing, breathability and ageing to BS EN 13859-1:2010 were carried out by a UKAS Accredited test house. Wind uplift testing was carried out by the Building Research Establishment to verify its suitability across all Wind Zones.

LABC Registered Details have been obtained using the new membrane in conjunction with insulation materials for buildups conforming to current Building Regulations requirements for Part L.

1. Double jeopardy: the potential for problems when bats interact with breathable roofing membranes in the UK.  S. Waring et al., Architecture and Environment, (2013), 1-13.


The functional breather membrane is UKCA marked in accordance with harmonised European Standard BS EN 13859-1 & 13859-2

tlx batsafe UKCA DOP



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