the present invention , which provides a non - asphaltic underlayment that is breathable , waterproof and skid resistant , and which encompasses tailorable breathability characteristics , will now be described in greater detail by referring to the following description and drawings that accompany the present application . in the accompanying drawings , like and / or corresponding elements are referred to by like reference numerals . fig1 - 4 of the present application illustrate various embodiments of the present invention . specifically , fig1 - 4 are cross - sectional views showing the non - asphaltic underlayment 10 of the present invention . fig1 illustrates a three - layer non - asphaltic underlayment 10 in accordance with a preferred embodiment of the present invention and which comprises a breathable thermoplastic film ( btf ) 14 bonded between a substrate 12 and spun - bonded or needle - punched or other types of non - woven fabrics 18 made from polypropylene , polyester , fiberglass or a blend of difference synthetic fibers . in fig2 , there is illustrated a two - piece non - asphaltic underlayment 10 that comprises a substrate 12 having a breathable thermoplastic film 14 bonded to a top surface 11 t of the substrate 12 . the substrate 12 is typically substantially non - waterproof . in this embodiment , the top surface including the breathable thermoplastic film 14 will face in a direction opposite of the roofing deck such that one or more shingles are laid - up directly on the breathable thermoplastic film 14 of the underlayment 10 . although fig1 shows the breathable thermoplastic film 14 on an upper surface of the substrate 12 , it is also contemplated in the present invention to have an underlayment in which the breathable thermoplastic film 14 is bonded on a bottom surface 11 b of the substrate 12 . fig3 shows an alternative embodiment of the present invention in which the substrate 12 is sandwiched between two - breathable thermoplastic films 14 using known techniques such as thermal , ultrasonic and / or adhesive bonding . that is , the top surface 11 t and bottom surface 11 b of the substrate 12 both include a breathable thermoplastic film 14 thereon . fig3 thus represents a three - piece underlayment . in fig4 , there is shown an embodiment in which a tie layer 16 is present between the substrate 12 and the breathable thermoplastic film 14 . the presence of the tie layer 16 improves the adhesion of the breathable thermoplastic film 14 to the substrate 12 . the tie layer 16 , which may also be referred to as a compatibilizer or a bonding agent , may be used in any embodiment of the present invention . if the adhesive bonding agent is non - breathable , it can be applied in discontinuous patterns , e . g . dots or squares . the substrate 12 employed in the present invention comprises an organic or inorganic reinforcement sheet or film that is capable of withstanding high ambient temperatures . the substrate is typically , but not always , non - waterproof . the reinforcement sheet or film can comprise a thermoplastic polymer or copolymer or a felt material . the substrate may be woven or non - woven , with preference given to a coated woven substrate for imparting superior mechanical properties in both machine and cross - machine direction . the substantially non - waterproof woven or non - woven substrate of the present invention is sometimes referred to in the art as a scrim . a woven substrate is preferable since it provides greater tensile and tear strengths compared with that of comparable non - woven substrate . no asphalt or other like bituminous material is present in or on the substrate 12 . illustrative examples of reinforcement thermoplastic polymeric materials that can be employed in the present invention as the substrate 12 include , but are not limited to : polyolefins , such as , for example , polyethylene ( high density , linear low density , low density or medium density ) and polypropylene ; polyethylene terephthalate ( pet ); polyamides ; polyvinyl chlorides ( pvc &# 39 ; s ); polystyrenes ; polyacrylics ; and any copolymers thereof . for purposes of definition herein , the term “ high density polyethylene ” denotes a polyethylene composition having a density of about 0 . 941 g / cc of higher ; the term “ medium density polyethylene ” denotes a polyethylene composition having a density of about 0 . 926 to about 0 . 940 g / cc ; and the terms “ low density or linear low density polyethylene ” denote a polyethylene composition having a density of about 0 . 90 to about 0 . 925 g / cc . of the various thermoplastic polymeric materials mentioned above , it is preferable to use a thermoplastic reinforcement material that comprises polyethylene , polypropylene or pet . the thermoplastic reinforcement material used as the substrate 12 is made using techniques well - known in the art . the substrate 12 may also be a felt material such as a cellulose fiber mat or a glass fiber mat . these types of substrates are made using techniques well known to those practicing the art . the substrate 12 may have any thickness associated therewith , but typically the thickness of the substrate 12 is from about 6 to about 60 mils . the substrate 12 is breathable and is usually , but not always , non - waterproof . in one embodiment , the breathable thermoplastic film 14 is a polyurethane based thermoplastic monolithic film ( or thermoplastic polyurethane ( tpu )). the polyurethane based thermoplastic film is a polymeric material obtained by first forming a prepolymer of polyether or polyester diols or polyols with excess diisocyanate and then chain - extending the prepolymer by reacting with a diamine or a diol . copolymers including the tpu are also contemplated as the breathable thermoplastic film 14 . suitable tpu &# 39 ; s that can be employed as the breathable thermoplastic film 14 are available from noveon ( esthane ®), merquinsa na inc . ( pearlthane ®/ pearlcoat ®), dow chemical company ( pellethan ®), basf ( elastollan ®), bayer ( texin / desmopan ®) or huntsman ( avalon ® or irogran ®). in another embodiment of the present invention , the breathable thermoplastic monolithic film 14 is an ethylene methacrylate ( ema ) copolymer ( such as elvaloy from dupont ), a polyolefin - based emac ( such as sp2220 from eastman chemical co . ), or an ethylene acrylic acid ( eaa ) based copolymer . these copolymer films offer similar properties as the tpu , i . e ., breathable and yet waterproofing . in yet another embodiment of the present invention , the breathable thermoplastic film 14 is a micro - porous polyolefinic ( polyethylene , polypropylene and other like polyolefins including copolymers thereof ) or polyester polymer which may or may not contain a filler therein . in yet another embodiment of the present invention , the breathable thermoplastic film 14 is a multilayered stack that includes any combination of above - mentioned breathable thermoplastic materials . the underlayment in accordance with the various embodiments of the present invention may take on , but are not limited to , the following forms and layer combinations : ( a ) micro - perforated coated woven scrim / micro - porous film / spun - bonded non - woven layer , ( b ) micro - perforated coated non - woven scrim / micro - porous film / micro - perforated coated woven layer , ( c ) micro - perforated coated woven scrim / micro - porous film . the combinations of micro - perforated fabric ( s ) and one or more micro - porous films may be bonded together by an adhesive or by thermal bonding , however , other known lamination techniques ( such as ultrasonication , adhesive or a combination thereof ) may be used , such that desired breathability can be tailored in to the composite structure . in the event that that such an adhesive is non - breathable , it can be applied in a discontinuous manner such as dots or squares , in which case the specific pattern with the number of such dots per unit area , and the spacing between them can be varied to design required breathability . the thickness of the breathable thermoplastic film 14 may vary , but typically it is from about 0 . 5 to about 10 mils , with a thickness from about 1 to about 3 mils being more highly preferred . thicker breathable thermoplastic films 14 are also contemplated . in embodiments in which a tie layer 16 is present , the tie layer 16 comprises a bonding agent , such as , for example , a polyamide , an ethylene copolymer such as ethylene vinyl acetate ( eva ), ethylene ethyl acrylate ( eea ), ethylene acrylic acid ( eaa ), ethylene methyl acrylate ( ema ) ( such as sp2207 , sp2403 , or sp1307 grades from voridian ) and ethylene normal - butyl acrylate ( enba ). however , the most - preferred material as a tie layer 16 is ema having a methyl acrylate level of about 18 % or greater . the tie layer 16 may be applied during formation of the substrate by including the bonding agent within the polymerization process , during the formation of the breathable thermoplastic film , or after substrate formation using one of the methods described below . the breathable thermoplastic film 14 may also be bonded to the substrate 12 by chemical bonding , mechanical bonding and / or thermal bonding . the breathable . thermoplastic film 14 may also be bonded using a nip such as that generated by a pair of heat calendar roll , or by using an ultrasonication chamber . in the case of polyolefinic based materials having filler induced micro - pores , those materials are made breathable upon stretching the film under appropriate conditions well known to those well versed in the art . in one embodiment , polypropylene with caco 3 fillers having micro - pores coated onto a glass mat is envisaged as a roofing underlayment that is breathable and yet waterproof . in order to improve the adhesion between filled or unfilled extrusion coated polyolefins such as polyethylene ( pe ) or polypropylene ( pp ) and glass mat — necessary for enhanced abrasion resistance — the following specific options are envisaged : ( 1 ) maleic anhydride grafted pp ( blended up to 10 %, but more preferably up to 5 %) to regular pp batch . magpp is commercially available from dupont ( as fusabond ®), atofina ( as lotadar ™ or orevac ™) and other vendors . ( 2 ) titanate or zirconate coupling agents such as those available from kenrich petrochemicals , inc . for improving the pp ( preferably with fillers such as carbon black ) bond to glass fibers . ken - react &# 39 ; s caps nz 12 / l ( zirconate based ) or caps l 38 / l ( titanate based ) at 5 % caps by weight of pp or lower , but more preferably 1 to 3 % by weight can be used . slight lowering of extrusion temperatures ( typically about 10 %) to create high shear for reactive compounding and dispersion of the titanate or zirconate masterbatch in the pp melt so that fiberglass mat can be subsequently coated uniformly . ( 3 ) in addition to ( 1 ) and ( 2 ) above , additional silane treatment to glass may become necessary as intimate mixing of glass fibers with pp ( as in an extruder ) cannot be done in composite process described herein . the well - known silane agents are aminoalkyltrialkoxysilanes such as 1 - dimethylaamino - 2 - propanol or 2 - dimethylamino - 2 - methyl - 1 - propanol or 3 - aminopropyl triethoxysilane in the presence of a salifying agent ( koh ) and an emulsifier such as polyoxyethylene octylphenyl ether . skid - resistance of polyolefinic coated underlayments can be increased by incorporating ethyl - vinyl acetate ( eva ) or modified eva such as maleic anhydride grafted eva ( like fusabond c series sold by dupont ) up to 10 % ( most preferably 1 - 3 %) by weight of pp . the underlayments of the present invention can also be coated or sprayed with an algaecide such as , for example , zinc powder , or copper oxide powder ; a herbicide ; an antifungal material such as micro - chek 11p ; an antibacterial material such as micro - chek 11 - s - 160 ; a surface friction agent such as byk - 375 , a flame retardant material such as ath ( aluminum trihydrate ) available from , e . g ., akzo chemicals and antimony oxide available from , e . g ., laurel industries and / or a coloring dye such as t - 1133a and iron oxide red pigments , and other products which can impart specific surface functions . the micro - chek products are available from the ferro corporation of walton hills , ohio . byk - 375 may be obtained from wacker silicone corporation of adrian , mich . and t - 1133a is sold by abco enterprises inc . of allegan , mich . the additional coatings of , e . g ., water repellent material , antifungal material , antibacterial material , etc ., may be applied to one or both sides of underlayment of the present invention . the waterproof and breathable underlayment 10 of the present invention is used as a component of a roofing system together with one or more conventional shingles . in this application , the underlayment of the present invention is first applied to the roofing deck and then secured thereto using securing means well - known to those skilled in the art , such as by nail or staple application . next , one or more shingles are laid - up on the uppermost layer of the underlayment 10 and thereafter the shingle is secured to the roofing deck . the lay up and securing steps are well - known to those skilled in the art . types of shingles that can be used in the present invention include , but are not limited to : asphalt - containing single or multi - ply organic or inorganic shingles . it is anticipated that the micro - perfed coated woven scrim layer 12 will be applied on a roof deck with layer 12 facing the roof and non - woven layer 18 as the exposed surface upon which roofers will walk . underlayment 10 applied in this manner provides a satisfactory frictional surface for roofer to walk on . alternatively the underlayment 10 can be flipped with micro - perfed coated scrim layer 12 on the upper exposed side coated with an anti - skid substance . the micro - perforations in underlayment 10 of the present invention are typically formed using pinned perforating rollers . the present invention is not , however , limited in the manner in which the micro - perforations are formed and other methods for perforation are contemplated , including : ( 1 ) perforation by heat embossing at temperatures over the melting point of the fiber ; ( 2 ) perforation by friction calendaring between an appropriately engraved and a smooth roller ; ( 3 ) perforation by slitting and extension perpendicular to the slits ; ( 4 ) perforation by passing male -/ female rollers ; ( 5 ) hot needle perforation ; and ( 6 ) perforation by water jets onto suitable supporting means such as coarse mesh screens or perforated drainage drums with projections in order to provide clear holes . the micro - perforations can be easily manipulated in shape ( e . g ., oval square , circular , etc . ), size ( e . g ., diameter , area ) and density so as to control the degree of breathability of underlayment 10 . other factors that influence the extent of perforations are pin density , diameter of the pins at the tips , pin height , and pin profile from the apex to the base . additionally , the pin tip ( apex ) can be of different shapes ( instead of circular ). alternatively , micro - perfing is possible by electrostatic perforation ( esp ) or laser - based techniques . the location of the pin roller can be varied as well . the pin roller may be temperature controlled depending on the line speed and material being perforated . a bank of pin rollers may be employed if necessary . the substrate , fabric or film may run against a support roller to provide additional stability and consistency of perforations . while the present invention has been particularly described and illustrated with respect to preferred embodiments thereof , it will be understood by those skilled in the art that the foregoing and other changes in forms and details may be made without departing from the spirit and scope of the present invention . it is therefore intended that the present invention is not limited to the exact forms and details described and illustrated .