surprising that such bicomponent fibers can satisfy the more rigorous requirements of a nib for a writing or marking instrument since the use of the other core polymers referenced in the 39 766 patent are not acceptable for this purpose as explained below it will also be understood that reservoirs formed of polyester nylon 6 6 fibers according to this invention are expected to have advantages even for use with nibs made of prior art materials to compare the properties of nibs made by this invention with nibs made of melt blown bicomponent polyester sheath fibers with different core materials square stock angularly cut nibs typical of marker u201c felt tip u201d pens were made from melt blown polyethylene terephthalate pet polypropylene pp 25 75 sheath core bicomponent fibers using the general techniques disclosed in the 39 766 patent cut with a razor blade at a 45 u00b0 angle and inserted into sanford king size item number 15000 permanent markers after the commercial nibs were removed this enabled testing in the exact ink and marker environment comparable products were made from melt blown bicomponent fibers comprising pet sheath materials covering respectively polybutylene terephthalate ticona pbt nylon basf ultramin and nylon 6 6 dupont zytel all samples spun well with the pet pbt and pet nylon 6 6 bonding acceptably pet nylon 6 bonding behavior was poorer than the other samples the pet nylon 6 nibs were attacked by the ink in a manner similar to pet pp because of this these pieces were not tested further samples were run at a variety of densities these densities all in g 10 pieces were pet pbt.