Mirrors for storage ring free-electron lasers in the vacuum ultraviolet must provide adequate reflectivity and resistance against synchrotron radiation. The free-electron laser system at ELETTRA (Trieste, Italy) is targeted to lase in the spectral range between 155 and 200\text{\hspace{0.17em} nm} . It was demonstrated that dense oxide multilayer coatings allow lasing down to 189.9\text{\hspace{0.17em} nm} . However, pure oxide systems show significant absorption at lower wavelengths and cannot be employed below 189.9 nm. Fluoride stacks can be deposited down to 130\text{\hspace{0.17em} nm} with high reflection values above 95\% , but their resistance against the harsh synchrotron environment is poor. They rapidly degrade; lasing cannot be realized with this mirror approach. For the range between 170 and 190\text{\hspace{0.17em} nm} , hybrid systems—combining fluoride and oxide materials—have been manufactured. With appropriate deposition procedures, mirrors achieve reflectance values up to 99\% and an adequate radiation resistance simultaneously. A mirror based on a conventional fluoride stack protected by a dense silicon dioxide protection layer was deposited and successfully employed for free-electron lasing at 176.4\text{\hspace{0.17em} nm} .