in the following a detailed description of embodiments will be given . it will be appreciated that the figures are for illustration only and are not in any way restricting the scope . thus , any references to direction , such as “ up ” or “ down ”, are only referring to the directions shown in the figures . one embodiment of a protective helmet comprises an energy absorbing layer , and a sliding facilitator being provided inside of the energy absorbing layer . according to one embodiment an in - mold helmet suitable for bicycling is provided . the helmet comprises an outer preferably thin , rigid shell made of a polymer material such as polycarbonate , abs , pvc , glassfiber , aramid , twaron , carbonfibre or kevlar . it is also conceivable to leave out the outer shell . on the inside of the shell an energy absorbing layer is provided which could be a polymer foam material such as eps ( expanded poly styrene ), epp ( expanded polypropylene ), epu ( expanded polyurethane ) or other structures like honeycomb for example . a sliding facilitator is provided inside of the energy absorbing layer and is adapted to slide against the energy absorbing layer or against an attachment device which is provided for attaching the helmet to a wearer &# 39 ; s head . the attachment device is fixated to the energy absorbing layer and / or the shell by means of fixation members adapted to absorb impact energy and forces . the sliding facilitator could be a material having a low coefficient of friction or be coated with a low friction material : examples of conceivable materials are ptfe , abs , pvc , pc , nylon , fabric materials . it is furthermore conceivable that the sliding is enabled by the structure of the material , for example by the material having a fiber structure such that the fibers slide against each other . during an impact , the energy absorbing layer acts as an impact absorber by compressing the energy absorbing layer and if an outer shell is used , it will spread out the impact energy over the energy absorbing layer . the sliding facilitator will allow sliding between the attachment device and the energy absorbing layer allowing for a controlled way to absorb the rotational energy otherwise transmitted to the brain . the rotational energy can be absorbed by friction heat , energy absorbing layer deformation or deformation or displacement of the at least one fixation member . the absorbed rotational energy will reduce the amount of rotational acceleration affecting the brain , thus reducing the rotation of the brain within the skull . the risk of rotational injuries such as subdural haematomas , sdh , blood vessel rupturing , concussions and dai is thereby reduced . fig1 shows a helmet according to one embodiment in which the helmet comprises an energy absorbing layer 2 . the outer surface 1 of the energy absorbing layer 2 may be provided from the same material as the energy absorbing layer 2 or it is also conceivable that the outer surface 1 could be a rigid shell 1 made from a different material than the energy absorbing layer 2 . a sliding facilitator 5 is provided inside of the energy absorbing layer 2 in relation to an attachment device 3 provided for attachment of the helmet to a wearer &# 39 ; s head . according to the embodiment shown in fig1 the sliding facilitator 5 is fixated to or integrated in the energy absorbing layer 2 , however it is equally conceivable that the sliding facilitator 5 is provided on or integrated with the attachment device 3 , for the same purpose of providing slidability between the energy absorbing layer 2 and the attachment device 3 . the helmet of fig1 has a plurality of vents 17 allowing airflow through the helmet . the attachment device 3 is fixated to the energy absorbing layer 2 and / or the outer shell 1 by means of four fixation members 4 a , 4 b , 4 c and 4 d adapted to absorb energy by deforming in an elastic , semi - elastic or plastic way . energy could also be absorbed through friction creating heat and / or deformation of the attachment device , or any other part of the helmet . according to the embodiment shown in fig1 the four fixation members 4 a , 4 b , 4 c and 4 d are suspension members 4 a , 4 b , 4 c , 4 d , having first and second portions 8 , 9 , wherein the first portions 8 of the suspension members 4 a , 4 b , 4 c , 4 d are adapted to be fixated to the attachment device 3 , and the second portions 9 of the suspension members 4 a , 4 b , 4 c , 4 d are adapted to be fixated to the energy absorbing layer 2 . the sliding facilitator 5 may be a low friction material , which in the embodiment shown is provided on outside of the attachment device 3 facing the energy absorbing layer 2 , however , in other embodiments , it is equally conceivable that the sliding facilitator 5 is provided on the inside of the energy absorbing layer 2 . the low friction material could be a waxy polymer , such as ptfe , pfa , fep , pe and uhmw pe , or a powder material which could be infused with a lubricant . this low friction material could be applied to either one , or both of the sliding facilitator and the energy absorbing layer , in some embodiments the energy absorbing layer itself is adapted to act as sliding facilitator and may comprise a low friction material . the attachment device could be made of an elastic or semi - elastic polymer material , such as pc , abs , pvc or ptfe , or a natural fiber material such as cotton cloth . for example , a cap of textile or a net could be forming an attachment device . the cap could be provided with sliding facilitators , like patches of low friction material . in some embodiments the attachment device itself is adapted to act as a sliding facilitator and may comprise a low friction material . fig1 further discloses an adjustment device 6 for adjusting the diameter of the head band for the particular wearer . in other embodiments the head band could be an elastic head band in which case the adjustment device 6 could be excluded . fig2 shows an embodiment of a helmet similar to the helmet in fig1 , when placed on a wearers head . however , in fig2 the attachment device 3 is fixated to the energy absorbing layer by means of only two fixation members 4 a , b , adapted to absorb energy and forces elastically , semi - elastically or plastically . the embodiment of fig2 comprises a hard outer shell 1 made from a different material than the energy absorbing layer 2 . fig3 shows the helmet according to the embodiment of fig2 when receiving a frontal oblique impact i creating a rotational force to the helmet causing the energy absorbing layer 2 to slide in relation to the attachment device 3 . the attachment device 3 is fixated to the energy absorbing layer 2 by means of the fixation members 4 a , 4 b . the fixation absorbs the rotational forces by deforming elastically or semi - elastically . fig4 shows the helmet according to the embodiment of fig2 when receiving a frontal oblique impact i creating a rotational force to the helmet causing the energy absorbing layer 2 to slide in relation to the attachment device 3 . the attachment device 3 is fixated to the energy absorbing layer by means of rupturing fixation members 4 a , 4 b which absorbs the rotational energy by deforming plastically and thus needs to be replaced after impact . a combination of the embodiments of fig3 and fig4 is highly conceivable , i . e . a portion of the fixation members ruptures , absorbing energy plastically , while another portion of the fixation members deforms and absorbs forces elastically . in combinational embodiments it is conceivable that only the plastically deforming portion needs to be replaced after impact . the upper part of fig5 shows the outside of an attachment device 3 according to an embodiment in which the attachment device 3 comprises a head band 3 a , adapted in encircling the wearer &# 39 ; s head , a dorso - ventral band 3 b reaching from the wearer &# 39 ; s forehead to the back of the wearer &# 39 ; s head , and being attached to the head band 3 a , and a latro - lateral 3 c band reaching from the lateral left side of the wearers head to the lateral right side of the wearer &# 39 ; s head and being attached to the head band 3 a . parts or portions of the attachment device 3 may be provided with sliding facilitators . in the shown embodiment , the material of the attachment device may function as a sliding facilitator in itself . it is also conceivable to provide the attachment device 3 with an added low friction material . fig5 further shows four fixation members 4 a , 4 b , 4 c , 4 d , fixated to the attachment device 3 . in other embodiments the attachment device 3 could be only a head band 3 a , or en entire cap adapted to entirely cover the upper portion of the wearer &# 39 ; s head or any other design functioning as an attachment device for mounting on a wearer &# 39 ; s head . the lower part of fig5 shows the inside of the attachment device 3 disclosing an adjustment device 6 for adjusting the diameter of the head band 3 a for the particular wearer . in other embodiments the head band 3 a could be an elastic head band in which case the adjustment device 6 could be excluded . fig6 shows an alternative embodiment of a fixation member 4 in which the first portion 8 of the fixation member 4 is fixated to the attachment device 3 , and the second portion 9 of the fixation device 4 is fixated to the energy absorbing layer 2 by means of an adhesive . the fixation member 4 is adapted to absorb impact energy and forces by deforming in an elastic , semi - elastic or plastic way . fig7 shows an alternative embodiment of a fixation member 4 in which the first portion 8 of the fixation member 4 is fixated to the attachment device 3 , and the second portion 9 of the fixation device 4 is fixated to the energy absorbing layer 2 by means of mechanical fixation elements 10 entering the material of the energy absorbing layer 2 . fig8 shows an alternative embodiment of a fixation member 4 in which the first portion 8 of the fixation member 4 is fixated to the attachment device 3 , and the second portion 9 of the fixation device 4 is fixated to inside of the energy absorbing layer 2 , for example by molding the fixation device inside of the energy absorbing layer material 2 . fig9 shows a fixation member 4 in a sectional view and an a - a view . the attachment device 3 is according to this embodiment attached to the energy absorbing layer 2 by means of the fixation member 4 having a second portion 9 placed in a female part 12 adapted for elastic , semi - elastic or plastic deformation , and a first part 8 connected to the attachment device 3 . the female part 12 comprises flanges 13 adapted to flex or deform elastically , semi - elastically or plastically when placed under a large enough strain by the fixation member 4 so that the second portion 9 may leave the female part 12 . fig1 shows an alternative embodiment of a fixation member 4 in which the first portion 8 of the fixation member 4 is fixated to the attachment device 3 , and the second portion 9 of the fixation device 4 is fixated to inside of the shell 1 , all the way through the energy absorbing layer 2 . this could be done for example by molding the fixation device 4 inside of the energy absorbing layer material 2 . it is also conceivable to place the fixation device 4 through a hole in the shell 1 from the outside of the helmet ( not shown ). fig1 shows an embodiment in which the attachment device 3 is fixated to the energy absorbing layer 2 at the periphery thereof by means of a membrane or sealing foam 24 , which could be elastic or adapted for plastic deformation . fig1 shows an embodiment where the attachment device 3 is attached to the energy absorbing layer 2 by means of a mechanical fixation element comprising mechanical engagement members 29 , with a self locking function , similar to that of a self locking tie strap 4 . fig1 shows an embodiment in which the fixating member is an interconnecting sandwich layer 27 , such as a sandwich cloth , which could comprise elastically , semi - elastically or plastically deformable fibers connecting the attachment device 3 to the energy absorbing layer 2 and being adapted to shear when shearing forces are applied and thus absorb rotational energy or forces . fig1 shows an embodiment in which the fixating member comprises a magnetic fixating member 30 , which could comprise two magnet with attracting forces , such as hypermagnets , or one part comprising a magnet and one part comprising a magnetically attractive material , such as iron . fig1 shows an embodiment in which the fixating member is re - attachable by means of an elastic male part 28 and / or an elastic female part 12 being detachably connected ( so called snap fixation ) such that the male part 28 is detached from the female 12 part when a large enough strain is placed on the helmet , in the occurrence of an impact and the male part 28 can be re - inserted into the female 12 part to regain the functionality . it is also conceivable to snap fixate the fixating member without it being detachable at large enough strain and without being re - attachable . in the embodiments disclosed herein the distance between the energy absorbing layer and the attachment device could vary from being practically nothing to being a substantial distance without parting from the concept of the invention . in the embodiments disclosed herein it is further more conceivable that the fixation members are hyperelastic , such that the material absorbs energy elastically but at the same time partially deforms plastically , without failing completely . in embodiments comprising several fixation members it is further more conceivable that one of the fixation members is a master fixation member adapted to deform plastically when placed under a large enough strain , whereas the additional fixation members are adapted for purely elastic deformation . fig1 is a table derived from a test performed with a helmet according having a sliding facilitator ( mips ), in relation to an ordinary helmet ( orginal ) without a sliding layer between the attachment device and the energy absorbing layer . the testis performed with a free falling instrumented dummy head which impacts a horizontally moving steel plate . the oblique impact results in a combination of translational and rotational acceleration that is more realistic than common test methods , where helmets are dropped in pure vertical impact to the horizontal impact surface . speeds of up to 10 m / s ( 36 km / h ) can be achieved both in horizontal and vertical direction . in the dummy head there is a system of nine accelerometers mounted in measure the translational accelerations and rotational accelerations around all axes . in the current test the helmets are dropped from 0 . 7 meter . this results in a vertical speed of 3 . 7 m / s . the horizontal speed was chosen to 6 . 7 m / s , resulting in an impact speed of 7 . 7 m / s ( 27 . 7 km / h ) and an impact angle of 29 degrees . the test discloses a reduction in translational acceleration transmitted to the head , and a large reduction in rotational acceleration transmitted to the head , and in the rotational velocity of the head . fig1 shows a graph of the rotational acceleration over time with helmets having sliding facilitators ( mips_350 ; mips_352 ), in relation to ordinary helmets ( org_349 ; org_351 ) without sliding layers between the attachment device and the dummy head . fig1 shows a graph of the translational acceleration over time with helmets having sliding facilitators ( mips_350 ; mips_352 ), in relation to ordinary helmets ( org_349 ; org_351 ) without sliding layers between the attachment device and the dummy head . please note that any embodiment or part of embodiment as well as any method or part of method could be combined in any way . all examples herein should be seen as part of the general description and therefore possible to combine in any way in general terms .
a helmet comprising an energy absorbing layer and a sliding facilitator is provided . the sliding facilitator is provided inside of the energy absorbing layer . a method of manufacturing a helmet comprising a sliding facilitator is further provided . the method comprising the steps of : providing an energy absorbing layer in the mould , and providing a sliding facilitator contacting the energy absorbing layer .