## 2 Materials and Methods  
The samples were cut with a custom-built mechanical cutting machine from 25 \(\upmu\)m thick FEP films (DuPontTM Teflon(r) FEP, Washington, WV, USA). The cutting was performed in two directions: parallel to or perpendicular to the roll direction. Small \"dogbone\"-shaped samples were used for microtensile tests with an overall length of 20 mm, a gauge length of 4 mm between the heads, and a width of 1 mm in the neck region. The radius of the shoulder was \(R=1\) mm, which yielded a gauge length of 2 mm of a constant cross-section. The effective length (\(L_{\textit{eff}}\)) that corresponds to the length of an equivalent sample having a constant cross-section in between the two sample heads was 3.515 mm [21]. The virgin samples (FEP-1) were subjected to heat treatment (FEP-2) for 30 min at a temperature of 200 \({}^{\circ}\)C (close to the maximum operating temperature) on a programmable POLOS Hotplate 200S (SPS, Bienenbuttel, Germany) with a uniform temperature of \(\pm 0.5\)\({}^{\circ}\)C; UV exposure (FEP-3) using the ABA class collimated solar simulator SF150B (Sciencetech Inc., London, ON, Canada), equipped with a Xenon short-arc lamp; and AM1.5G filter (irradiance--1.13 mW/cm\({}^{2}\) @ 254 nm and 3 mW/cm\({}^{2}\) @ 365 nm, exposure time--72 h), as well as the combination of heat treatment and UV exposure (FEP-4). X-ray diffraction data were collected using a D8 Discover X-ray diffractometer (Bruker AXS GmbH, Karlsruhe, Germany) with a Cu K\({}_{\alpha}\) (\(\lambda\)= 1.54 A) X-ray source. Parallel beam geometry with a 60 mm Gobel mirror (i.e., an X-ray mirror on a high-precision parabolic surface) was used. This configuration enables the divergent incident X-ray beam to be transformed from a line focus of the X-ray tube into a parallel beam that is free of K\({}_{\beta}\) radiation. The primary side also had a Soller slit with an axial divergence of 2.5\({}^{\circ}\). The secondary side had a LYNXEYE (1D mode) detector with an opening angle of 2.160\({}^{\circ}\) and a slit opening of 6.0 mm. The voltage and current of the X-ray generator were 40.0 kV and 40 mA, respectively. Coupled 2\(\theta\)/\(\theta\) scans were performed in the range of 3.0-30.0\({}^{\circ}\) with a step size of 0.016\({}^{\circ}\), a time per step of 19.2 s, and an auto-repeat function enabled. The processing of the resultant diffractograms was performed with DIFFRAC.EVA V7 software. Macromolecular orientation texture analysis was performed to describe the variation in pole density (determined by the intensity of the diffracted X-ray beam) with pole orientation for crystalline component reflection at 17.69\({}^{\circ}\) in 2\(\theta\). Data were collected using a standard mode (unlocked coupled) with 5\({}^{\circ}\) of \(\delta\) measured for a full circle 0-360 incr. 5\({}^{\circ}\) in the Phi (\(\varphi\)) range and 0-60 incr. 10\({}^{\circ}\) in the Psi (\(\varphi\)) range. The measured data were corrected for background scattering and beam defocus using the Diffracplus MULTEX 3 software package. The mechanical properties of the FEP film samples were investigated with a custom-built tripod design uniaxial microtensile tester, which is described in previous work [22]. The piezo-actuated microtensile setup was able to measure film elongation up to 210 \(\upmu\)m with an accuracy of 50 nm. The total strain applied during the tensile tests was 5%. The strain rate of the tensile experiments was 4.8 \(\upmu\)m/s. The registration of the force and displacement of the samples was carried out during the tensile tests. The force of tension was applied parallel and perpendicular to the principal orientation direction of the FEP films. During the tensile test, five samples were investigated for each different processing condition. Each sample was loaded and unloaded, and the mean values of Young's modulus and yield stress were obtained as an average of five tested samples. Values are reported as means \(\pm\) standard error of the mean.