Having spent a lot of time over the last 18 months actually measuring the different amounts of force to separate prints in different resin materials from various surfaces you might want to consider the following findings:
1: FEP - V - PDMS . Resin adheres to FEP better than to PDMS (For a given surface area of 100mm2) the adhesion to FEP is between 1.3 and 1.8 times greater. The adhesion of PDMS to the resin gets less as the PDMS degrades due to UV light exposure.
2: FEP outlasts PDMS by a factor of approx. 180 to 1 (Its usefulness being defined as when it either degrades to 95% of the UV energy being transmitted through it compared to when the material is first used) - Think of the milky appearance of PDMS after its been used in a printer for a while. The milky appearance both lowers UV transmission rate and also causes diffusion, therefore a print will not be so sharp after a period of time…
3: Both FEP and PDMS need significantly less force in a shear motion to separate from the print rather than a simple (tensile force) pull.
4: Our conclusion is that a shear force combined with a small tensile pull results in the lowest force required to separate a print from either PDMS or FEP. Both forces should be applied at a similar speed with the tensile force being approx. 45% of the shear force applied for optimal separation.
5: The roller tension method deployed on the Form 3 is not greatly different to the system used by Asiga on its printers (albeit that Asiga started to use that method years before Formlabs).
6: In our opinion FEP is significantly better for the average printer use than PDMS in a typical working environment and is the most cost effective.