The above polishing layer is preferably constituted with a polymer material having {HEAD ~ a tensile elastic modulus} at {TAIL ~ 50° C.} after saturation swelling with water at 50° C. of 130 to 800 MPa, a loss tangent at 50° C. of 0.2 or less, and a contact angle with water of 80° or less 
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The above polishing layer is preferably constituted with a polymer material having { HEAD ~ a tensile elastic modulus } at { TAIL ~ 50 ° C. } after saturation swelling with water at 50 ° C. of 130 to 800 MPa , a loss tangent at 50 ° C. of 0.2 or less , and a contact angle with water of 80 ° or less
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