They used a German hardwax designed for exteriors, just a clear finish (no colour in the stain). The brand they used is called OSMO. We use a similar product with a different brand name now, here, called Saicos (the two products are interchangeable, though if you choose to use a colour, the colour swatches may not be exactly the same. There are other hardwax type finishes available as well. It stands up well and is easy to apply, in addition to being eco-friendly and non-toxic. If you would like information on this type of stain, a quick search of "hardwax vs urethane" will bring up plenty of discussions about the specific characteristics and application methods. You can also just give us a call!