A window for a display device comprising: a plastic substrate and a hard coating layer disposed on at least one side of the plastic substrate, wherein the plastic substrate has a yield strain of greater than or equal to 0.8 % at 85 degrees Celsius and 85 % relative humidity, wherein the yield strain is measured according to the method in the description, wherein the plastic substrate has a thickness of 25 micrometers to 100 micrometers, and wherein the plastic substrate comprises a poly(imide-amide) copolymer including an imide unit and an amide unit, wherein the imide unit consists of a first repeating unit represented by the following Chemical Formula 1-1 and a second repeating unit represented by the following Chemical Formula 1-2: wherein A 1-1 is represented by the following formula: wherein L is a single bond, -O-, -S-, -C(=O)-, -SO 2 -, -Si(CH 3) 2 -, or - (CR' 2) p - wherein 1≤p≤10, and R' is hydrogen, a hydroxy group, a C1 to C3 alkyl group, or a C1 to C3 fluoroalkyl group), A 1-2 is represented by the following formula: and A 2 is represented by the following formula: wherein the amide unit comprises a moiety represented by Chemical Formula 2: wherein in Chemical Formula 2, A 3 is a moiety selected from a substituted or unsubstituted divalent C5 to C24 aliphatic cyclic group, a substituted or unsubstituted divalent C6 to C24 aromatic ring group, a substituted or unsubstituted divalent C4 to C24 hetero aromatic ring group, and -L-SiR 2 -O-SiR 2 -L- wherein L is a single bond or a C1 to C10 alkylene group and R 2 is a C1 to C10 alkyl group, wherein the aliphatic or aromatic ring group is present alone; two or more rings are fused to each other to provide a polycyclic aromatic ring; or the two or more aliphatic rings or the two or more aromatic rings are linked through a single bond, -O-, -S-, -CO-, -CH -, -SO 2 -, - Si(CH 3) 2 -, -(CH 2) p - wherein 1≤p≤10, -(CF 2) q - wherein 1≤q≤10, a C1 to C10 divalent alkylene group having at least one substituent selected from a C1 to C10 linear or branched aliphatic hydrocarbon group, a C1 to C10 fluoroalkyl group, a C6 to C20 aromatic hydrocarbon group, and a C6 to C20 alicyclic hydrocarbon group, or -C(=O)NH-, and A 4 is a substituted or unsubstituted divalent phenylene residual group, a substituted or unsubstituted divalent naphthalene residual group, or a residual group where two substituted or unsubstituted aromatic rings are linked through a single bond, -O-, -S-, -C(=O)-, -SO 2 -, -Si(CH 3) 2 -, -(CR' 2) p - wherein 1≤p≤10, R' is hydrogen, a hydroxy group, a C1 to C3 alkyl group, or a C1 to C3 fluoroalkyl group), or (CF 2) q wherein 1≤q≤10. a plastic substrate and a hard coating layer disposed on at least one side of the plastic substrate, wherein the plastic substrate has a yield strain of greater than or equal to 0.8 % at 85 degrees Celsius and 85 % relative humidity, wherein the yield strain is measured according to the method in the description, wherein the plastic substrate has a thickness of 25 micrometers to 100 micrometers, and wherein the plastic substrate comprises a poly(imide-amide) copolymer including an imide unit and an amide unit, wherein the imide unit consists of a first repeating unit represented by the following Chemical Formula 1-1 and a second repeating unit represented by the following Chemical Formula 1-2: wherein A 1-1 is represented by the following formula: wherein L is a single bond, -O-, -S-, -C(=O)-, -SO 2 -, -Si(CH 3) 2 -, or - (CR' 2) p - wherein 1≤p≤10, and R' is hydrogen, a hydroxy group, a C1 to C3 alkyl group, or a C1 to C3 fluoroalkyl group), A 1-2 is represented by the following formula: and A 2 is represented by the following formula: wherein the amide unit comprises a moiety represented by Chemical Formula 2: wherein in Chemical Formula 2, A 3 is a moiety selected from a substituted or unsubstituted divalent C5 to C24 aliphatic cyclic group, a substituted or unsubstituted divalent C6 to C24 aromatic ring group, a substituted or unsubstituted divalent C4 to C24 hetero aromatic ring group, and -L-SiR 2 -O-SiR 2 -L- wherein L is a single bond or a C1 to C10 alkylene group and R 2 is a C1 to C10 alkyl group, wherein the aliphatic or aromatic ring group is present alone; two or more rings are fused to each other to provide a polycyclic aromatic ring; or the two or more aliphatic rings or the two or more aromatic rings are linked through a single bond, -O-, -S-, -CO-, -CH -, -SO 2 -, - Si(CH 3) 2 -, -(CH 2) p - wherein 1≤p≤10, -(CF 2) q - wherein 1≤q≤10, a C1 to C10 divalent alkylene group having at least one substituent selected from a C1 to C10 linear or branched aliphatic hydrocarbon group, a C1 to C10 fluoroalkyl group, a C6 to C20 aromatic hydrocarbon group, and a C6 to C20 alicyclic hydrocarbon group, or -C(=O)NH-, and A 4 is a substituted or unsubstituted divalent phenylene residual group, a substituted or unsubstituted divalent naphthalene residual group, or a residual group where two substituted or unsubstituted aromatic rings are linked through a single bond, -O-, -S-, -C(=O)-, -SO 2 -, -Si(CH 3) 2 -, -(CR' 2) p - wherein 1≤p≤10, R' is hydrogen, a hydroxy group, a C1 to C3 alkyl group, or a C1 to C3 fluoroalkyl group), or (CF 2) q wherein 1≤q≤10.