XYlink HER is an aromatic diol chain extender with symmetrical molecular structure. Its structure regularity is less than its isomer HQEE because of two hydroxyethyl groups located on the benzene ring of 1,3-site (meta-). The melting point of HER is lower than HQEE, and the crystallization speed is slower than HQEE and MOCA. The pot-life of HER cured PU system is longer than that of butanediol system. The workability of XYlink HER is good.