Reflective / Refractive **Ice** It does not need to be water made. It should have high reflection. As an additional benefit, when the laser hit, it will create gas that will further absorb/distort the laser and hide you. You might want to have multiple layers for [different wavelengths][1] / a way to adjust depending on the wavelength used. As an additional benefit, your ship would end up looking like a [comet][2] when hit ;) [1]: https://en.wikipedia.org/wiki/Reflectance [2]: https://en.wikipedia.org/wiki/Comet