Cover film

A cover film used for covering a test subject on a substrate, the cover film comprising:

• a support;
• and
• a polymer layer containing a polymer that includes a repeating unit derived from an alkyl acrylate having an alkyl group having 1 to 15 carbon atoms and a repeating unit derived from an alkyl methacrylate having an alkyl group having 1 to 15 carbon atoms,
• wherein a fracture toughness value of the polymer layer is 0.2 MPa·m0.5 or more,
• an in-plane retardation of the support at a wavelength of 590 nm is 1,000 nm or less, and
• a requirement 1 and a requirement 2 are satisfied,
• the requirement 1:
• a dissolution rate of the polymer layer in xylene is 0.01 to 0.25 g·m−2·s−1,
• the requirement 2:
• in a case where a viscosity of a xylene solution having a concentration of solid contents of 20%, which is obtained by dissolving the polymer layer in xylene, at 25° C. is defined as X, 1/X is 0.005 to 0.060 cp−1.