The good thing about TIFFs is they can compress quite well but arent "lossy" like JPEGs, that is repeated opening, editing and resaving doesnt cause degradation. TIFFs also save an alpha channel when you render in Poser (so do PNGs), so the background can be made transparent in a paint package like Photoshop or Paintshop Pro - useful for compositing or multiple figure renders on low-memory PCs, like mine. When Poser uses them they probably use the same amount of memory as any other format but take more hard drive space to save. They are lousy at zipping, sometimes ending up bigger! TIFFs are our friends B)