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A CRITICAL REVIEW OF IMPACT RESISTANT MATERIALS USED IN SPORTSWEAR
CLOTHING
Tyler, D., and Venkatraman, P.D.,
Manchester Metropolitan University, Manchester, UK
Email for correspondence: p.venkatraman@mmu.ac.uk
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Abstract
This paper highlights the significance of impact resistant materials which are incorporated in
sportswear and functional outdoor applications. In recent years, there have been interesting
explorations on a wide range of composite materials such as coir/EVA as nonwoven impact
protectors, polypropylene and flax fibre laminate, cellular textile materials as sports protectors for
helmets. 3D spacer fabrics were explored by Dow Corning on varying thicknesses and levels of
protection. In addition materials such as, D3O and visco-elastic polymer dough were also reported to
have potential in sportswear applications such as the market for knee pads. In addition, Dow
Corning's helical auxetic system is made up of an inelastic fibre spirally wound around a thicker
elastic fibre that expands to absorb the shock while the inelastic one limited the expansion. Some
concerns noted by researchers are that it has limited applications and the benefits of the impact
resistant materials should be evaluated using precise monitoring systems.
In this context, the authors have critically evaluated the literature, explored the importance of such
materials in the context of functional clothing used for sportswear, and reported their limitations and
implications. The study also is informed by experimentation using a custom-built measurement device
to precisely monitor the pressure profile of various materials. This device is modelled on some of the
ISO test procedures for assessing impact protection. The pressure sensors are located below the
sample material and forces transmitted through the material by an impactor are recorded in the form
of a load-vs-time dataset. Quantitative comparisons of a range of commercial materials used for
impact protection have been obtained.
Background and rationale
Recently there has been a surge in the sports wear market for low levels of impact protection
particularly in games such as baseball, hockey, football, cricket, etc., and medium level impact
protection on functional wear such as personal protection equipment. The main focus of this paper is
to highlight the significant importance of impact resistant materials which are incorporated in
sportswear and functional outdoor applications. The study disseminates a recent experimentation
using a custom-built measurement device to precisely monitor the pressure profile of various
materials. This device was modelled on some of the ISO test procedures (BS7928:2009) for assessing
impact protection materials.
There has been a considerable amount of literature (Shishoo, 2005) on sportswear products discussing
on performance such as comfort, durability, functionality, etc. However there is a shortage of
information relating to materials which are used for preventing from injuries sustained in sport related
activities. This includes the level of impact or force sustained at the point of contact, capabilities of
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absorbing the shock without causing injury to the wearer, practicality of use in sportswear apparel and
clothing.
In the UK there is a great deal of interest amongst younger adults to get involved in sport or leisure
activities. Different sports require different performance characteristics depending upon the level of
activity, the intensity of sport played – amateur or professional and whether it is played indoor or
outdoor. In recent times there has been an increase in the number of people who involve in sport
related activities (recreational, leisure activities). Sport England (formerly known as English Sport
Council, 2011) which reported that during April 2010/11 that in the UK 6.9 million adults (above age
16) have had participated in sport activities three times a week for 30 minutes at moderate intensity.
This report reveals that the participation increased by 108,600 since 2007/08.
National sports medicine institute, NSMI (www.nsmi.org.uk) stated that several sports players endure
injuries that are caused by impact or contact with objects, surfaces or other people. Injuries caused by
impact and contact are common sports such as football and rugby and more dangerous sports such as
motor racing, boxing and skiing. Often, contact with other people can cause an athlete to become off
balance, or change direction quickly; this causes damage to the connective tissue; powerful direct
contact may also cause a joint to become displaced. Impact injuries usually include spinal injuries,
ligament and tendon damage, fractures and head and spinal injuries. They also added that although
injuries are a part and parcel of contact sports; measures if taken appropriately would reduce the
likelihood of suffering from an injury. Protective clothing is often worn in more dangerous sports to
protect the body from injury; this can often be seen in rugby and boxing. Some of the common
injuries in most widely played sport activities are:
Cricket
• Head injuries to batsmen caused by fast bowling
• Bowlers are at risk of back injuries (muscle strains) due to the repetitive and sometimes
awkward movements involved when bowling.
• Fieldsmen getting injured during fall or collision.
• Knee damage and strain is also common.
Football
• Fractures
• Cuts and bruises
• Boot-stud injuries
• Knee damage and strain due to repetitive twisting
• Ankle injuries
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Racquet Sports
• Tennis elbow
• Fractures caused by falling on hard surfaces
• Muscle strains through repetitious movement
• Frozen Shoulder caused by overhead movements
Impact injuries can damage to the connective tissue, and cause superficial injuries such as cuts,
bruises, and most fractures which can be treated with simple medication and will heal over time;
however head and spinal injuries should be treated as emergency medical condition.
A range of composite materials such as coir/EVA as nonwoven impact protectors (Maklewska et al.,
2005), polypropylene and flax fibre laminate (de Velde et al., 1998), cellular textile materials (Tao
and Yu, 2002) as sports protectors for helmets. In addition, 3D spacer fabrics were explored by Dow
Corning on varying thicknesses and levels of protection (Dow Corning, 2011). Researchers
(Maklewska et al., 2002) compared the impact strength of nonwoven fabric pads intended for
applications in protective clothing and sportswear. A Schob pendulum elastometer measured fabric
resilience. An Instron tensile testing machine determined changes in deformation in relation to load.
The 40 millimetre thick single layer, three-dimensional fabric exhibited a high relative absorption rate
and low impact force, but was too thick for use in protective pads. The 20-millimetre thick multilayer
fabric was more suitable. Researchers added that future research would address the manufacture of
multilayer protective pads with a variety of fabrics having different properties.
Cushioning technology provider Roger Co. have reported two customisable products using its Poron
XRD material (WSA, 2011), two versions were highlighted extreme impact pad and B-guard. The X-
pad was recommended for knee and elbow pads to shin and thigh protection. The product has fabric
backing that allows moisture wicking air channels to enhance comfort.
Table 1 Examples of materials used in sports wear for impact protection
S.No Name of the
material
Source Relevance Remarks
1 Sorbothane Sorbothane.co.uk Shoe insoles for
absorbing shock
A synthetic visco
elastic polymer
3
Kryton 10
Gilbertrugby.com Triflex padding
system
Gilbert PE foam
4
Canterbury
Flexitop vest,
Body Armour Impact protection PE foam
5 Kooga EVX V Kooga-rugby.com Pads for a wide
range of
Padding EVA
(ethyl vinyl
5
sportswear acetate)
6
POC-U
Can be moulded
into various
shapes
Visco-elastic
polymer dough –
pol
y
urethane foam
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Force field body
armour
Forcefieldbodyarmour.com Nitrex EVO
A family name for
the PVC Nitrile
materials used in
triangular grid
form.
Materials and Methods
Whilst there are many standard test methods, the emphasis is not on materials, but on the efficacy of
Personal Protective Equipment (PPE). The driver is safety because commercial products need to
achieve a specified level of protection for the wearer. Many of these tests relate to headwear: for
industrial working environments and for a wide variety of sporting activities. Two of these tests have
informed the design of the test equipment used.
Industrial bump caps
BS EN 812:1997/A1:2001: Industrial bump caps are intended to protect the wearer’s head from the
effects of bumping against hard, stationary objects with sufficient severity to cause laceration or other
superficial injuries. The striker for measuring impact protection is a 5 kg mass with a flat striking
face with 10 cm diameter. This falls onto a head form to which the force transducer is attached. The
impact energy is nominally 12.5 J and impact protection is related to the maximum force transmitted
to the head form. The upper limit for passing the test is 15.0 kN.
Specification for head protectors for cricketers
BS 7928:1998: In this case, the falling head form method is used, because the wearer is anticipated to
provide movement that will affect the impact experienced. The head form, with the helmet fitted, is
raised above a fixed anvil and dropped to generate the impact. The test equipment incorporates a tri-
axial accelerometer to record the deceleration of the head form in all three directions, and a resultant
value is recorded. The test data allows the calculation of the head injury criterion (a measure of the
expected likelihood of serious injury to the user). The anvil is normally a cricket ball-sized object, but
a flat surface or a simulated kerbstone may also be used. The impact energy is normally set to 15 J
and the maximum deceleration of the striker is 250g (where g=9.81m/s2)
Both these tests involve a striker falling on a surface, with the protective product experiencing the
impacts. As our research concerns material properties, measurement of deceleration are of less
interest. Consequently, we have focused attention on the forces experienced by the transducer
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attached to the anvil which is under the protective material. The test equipment has a striker, a steel
ball, falling on to a flat anvil on which the protective material is placed. The pressure sensors are
located below the sample material and the forces transmitted through the material by the impactor are
recorded in the form of a load-vs-time data set. By varying the diameter of the ball, different impact
profiles can be created. The mass/height of fall parameters determines the impact energy. For
research purposes, impacts of 5J, 10J and 15J are used. An illustration of the test equipment is in
Figure 1.
Table 2 Summary of materials used in this research
Sample
number
Material Thickness
(mm)
Density (g/cm3) Note
1 GPhlex 8.5 0.0025 A proprietary material sourced
from collaborator
2 D3O - Dilatant material absorbs shock
3 Poran XRD 7.63 0.0005 Open cell urethane foam
4 EVA foam 5.1 0.0003 A cross-linked closed cell
polyethylene foam
4 Leather 2.7 0.0008 Unfinished leather (cow)
Base plate
signal
processor
Amplifier
Sacrificial plate
Stand
1 m tower guide
A 5 cm steel ball
dropped 1m from
test sample (5J
impact)
Sensor captures
the impact force
transmitted through
the sacrificial plate
Test sample
Support structure
Floor lev el
Figure 1 Illustration of impact measuring testing device
In the tests reported here, all the materials received the same low energy 5J impacts. A typical set of
results recorded for a thin (3 mm) material is illustrated in Figure 2. There was insufficient energy
taken out by the material, so the ball made a few bounces before coming to rest, and these movements
are apparent in the test data.
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02468101214161820
Time (ms)
-2
0
2
4
6
8
10
12
14
Force (kN)
Figure 2 Impact forces experienced under a 3mm layer of Poron XRD (Peak force = 12.7 kN).
The materials tested were Poron XRD, D3O, GPhlex, EVA foam and a sample of unfinished leather.
Poron XRD and D3O are market leaders for providing protection from impacts and are in widespread
commercial use. GPhlex is a similar material but not yet in widespread commercial use. The EVA
foam was derived from a Canterbury rugby shirt, and the leather was a sample of unfinished material
obtained from cow skin. Samples of materials of different thicknesses were prepared with dimensions
of 100 x 100 mm. Thicknesses were measured using a Shirley thickness tester.
Poron XRD is open cell urethane foam. When at rest above the glass transition temperature of the
urethane molecules, it has softness and flexibility. When impacted quickly, the glass transition
temperature of the material drops so that the urethane molecules stiffen to protect the wearer from
damage.
D3O is comprised of a polymer composite which contains a chemically engineered dilatant, an energy
absorber. This basic material has been adapted and enhanced to meet specific performance standards
and applications. The material is soft and flexible in its normal state, however when impacted by force
it locks itself and disperses energy and returns to its normal state.
Ethylene vinyl acetate (EVA) foams are described as a specific type of cross-linked closed cell
polyethylene foam. They are designed to be soft, with a rubber-like texture and with good shape
recovery after deformation.
Findings
Quantitative comparisons of a range of commercial materials used for impact protection have been
obtained using the “Peak Force” parameter. The five materials selected for analysis are: Poron XRD,
D3O, GPhlex, EVA Foam and unfinished leather. All have been subjected to 5J impacts using a 50
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mm diameter steel ball. The mean peak forces are plotted against the thickness of the material in
Figure 3.
Figure 3 Peak force variations with material thickness
As a general point, where the peak forces were above about 10 kN, it was found that the materials
were damaged in some way – usually identified by the presence of a hole. Peak forces lower than 10
kN sometimes left a surface mark, but more usually the material was elastically deformed and there
was no visible sign of an impact.
Discussions
Four of the materials tested are commercial products designed to provide impact protection to the
human body. The fifth is an untreated leather sample with a thickness of 3mm. This natural material
is included among these materials for comparison purposes.
(a) Thickness effects
The reduction in peak force with thickness is entirely predictable, because all these materials absorb
energy when impacted. Samples of 10mm thickness or more are effective in protecting against 5J
impacts and the impacting sphere produces no surface damage. However, differences are apparent.
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At 15 mm thickness, all the synthetic materials provide good protection at a level significantly better
than 5 layers of the leather. The energy absorption capabilities of the synthetics appear to be
comparable.
At 10 mm thickness, the EVA Foam is similar to an equivalent thickness of leather but the peak forces
observed are about twice those obtained with Poron XRD, D3O and GPhlex. This suggests that EVA
Foam has an internal structure that collapses more easily, reducing the performance of thinner
samples.
With the 5mm thickness samples, there are three types of behaviour. D3O and GPhlex are the best
performing materials. Poron XRD behaves much the same as leather, and the EVA Foam provides
very little protection. 5mm thickness materials are important when considering the selection of
materials for protective garments, particularly sportswear where the goal is not to restrict the athlete
(wearers do not like thick and bulky inserts).
For 2 and 3mm thicknesses, those materials that have been tested do not show protection capabilities
that are significantly better than leather.
(b) Garment design
If product designers are able to use 15 mm materials to provide protection, then their task is relatively
easy, as the available materials all appear to be effective. Decisions about which material to use can
be made on other grounds: cost, flexibility, comfort, ease of fabrication, etc.
The decision about which 10 mm thickness material to use has to recognise that the energy absorption
properties vary considerably. It is not enough to know that a material is capable of absorbing energy
– the issue is whether 10 mm provides the intended protection.
5mm thickness materials are important when considering the selection of materials for protective
garments, particularly sportswear, where the goal is not to restrict the athlete (wearers do not like
thick and bulky insert in their garments). Some products have been examined that suggest this issue
is commercially important. Three leading rugby shirt brands offer products with impact protection,
and all of them use an EVA Foam. In the shoulder region, the thickness is 10mm whereas the upper
arms have 5mm thickness. Recent feedback from rugby players is that the shoulder protection is
uncomfortable and restrictive. The laboratory tests suggest that the shoulder protection is less
effective than it could be if other materials were used, and also that the 5mm upper arm protection is
of little benefit to the wearer.
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For 2 to 3mm thicknesses, product designers should realise that materials do not perform effectively
and that the alternative of using a leather component of the garment may provide the same protection
but have other advantages for the garment in use. This is an interesting area of research and we intend
to look more closely at different types of leather and products that are engineered to have enhanced
energy absorption at 3mm thickness.
Summary
Impact protection materials for sports wear clothing had been in gradual increase in sports such as
rugby, cricket, hockey, etc, as sportsmen and women take intensive participation in sporting events.
Critical review highlighted the range of materials available and the test standards, such as, industrial
bump caps, BS EN 812:1997/A1:2001 and specification for head protectors for cricketers, BS
7928:1998 for measuring impact forces. Both these tests involved a striker falling on a surface, with
the protective product experiencing the impacts. In this paper as the focus was on material properties,
measurement of deceleration was of less interest. The force experienced by the transducer attached to
the anvil which is under the protective material was measured. Five different materials were tested
Poron XRD, D3O, GPhlex, EVA foam and a sample of unfinished leather. All have been subjected to
5J impacts using a 50 mm diameter steel ball. Figure 2 illustrated that peak force above 10 kN
induced surface damage of the test samples.
Samples of 10mm thickness or more were effective in protecting against 5J impacts and the impacting
sphere produced no surface damage. Bulky inserts and heavy protective pads restricted free
movement of sports person; hence much focus was directed to product performance at 5mm samples.
D3O and GPhlex were the best performing materials (5mm). Poron XRD behaved much the same as
leather, and the EVA Foam provided very little protection. Leather with 3mm performed much better
than the commercially available materials. This experimentation using the custom built equipment
provided the basis for measuring the impact forces passing through the material. It also unearthed the
possibilities of exploring a wide range of natural and synthetic materials for sportswear impact
protection. Subsequent stages of research will consider design principles for materials that will
perform better at low levels of thickness and explore various garment designs using different formats
of materials for impact protection used for sportswear.
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References
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