Probably sodium polyacrylate, very water absorbant polymer, 90% or more water when fully hydrated. Most of the water is available to plant roots. They look like a plastic bead when dry, and like a much larger sphere of gelatin when wet. Naturally colorless, you often find them with colors added to be more decorative in glass vases for cut flowers or in craft projects. Harmless when used properly, but I would question their use with any orchids that don't like to stay wet. You can get the same product in powdered rather than bead form, often used by mixing in potting soil. For orchids the bead form probably makes sense, but either way once it is in the potting mix you aren't going to get it out, so it isn't really useful as a short-term one week away situation.