premise: expanded polystyrene looks like a rigid white foam and is used as packing or insulation
hypothesis: polystyrene is best characterized as a kind or type of honey locust (or Gleditsia triacanthos), defined as 'tall usually spiny North American tree having small greenish-white flowers in drooping racemes followed by long twisting seed pods; yields very hard durable reddish-brown wood; introduced to temperate Old World' .