Honeybees collect resinous substances from certain plants and trees. This is called propolis and they collect it onto their pollen baskets looking like little shiny blobs. It's a mystery to me how they handle it without getting all stuck up because it's very difficult to remove from hands and clothing. In the hive it's used as a general purpose sealer and gap filler which has the added advantage of being anti-bacterial. In the video the propolis is stretchy and sticky but at low temperatures it becomes hard and brittle.The bees also add it to beeswax making it much stronger so they can use it as bridging comb where comb support is needed.