between about 0 05 and about 5 with respect to the modified binder and is a polysiloxane having repeating units of u2014 si u2014 o u2014 the siloxane polymer can be modified with various substituents which include linear branched or aromatic end groups optionally containing oxygen sulfur and or nitrogen generally the present polysiloxanes are classified as polyalkyl polyaryl polyalkylaryl and polyether siloxanes the polysiloxanes found to be most useful in the present invention are those having a weight average molecular weight of at least 600 the polysiloxanes listed in following table 1 are representative the modified binder of the present invention alters the interfacial effect between the mat and a surface coating which promotes fiber u201c pull out u201d during force applied to prevent immediate fiber breaking or tearing which occurs during separation of portions of the coated mat when the modifier is omitted it is believed that the increased tear strength of the composite is due to an interfacial interaction between the coating and the mat containing the present modified binder which dissipates the force applied for separation the accompanying drawing is a top plan view illustrating the separation of a composite which comprises a glass fiber mat having an asphalt coating which penetrates the mat the portions of the coated mat being separated are indicated by 2 and 4 with fibers 11 bridging the separated area and resisting disunion before total separation occurs for the manufacture of roofing shingles or bur a polysiloxane containing fiberglass mat with a urea formaldehyde binder and the present crosslinked polymer modifier is preferred the dried cured mat may be covered on one or both sides with a conventionally thick coating of a standard asphalt or asphalt compound to produce a composite.