Ultem Material?
The short of it: Ultem is very durable material with an amber color. It is very similar to the Dunlop Ultex material and has great tone and feel on guitar.
The scientific stuff: Utlem (Polyetherimide) is an amorphous, amber-to-transparent thermoplastic with characteristics similar to the related plastic PEEK. When comparing PEI to PEEK, the former is cheaper but has lower impact strength and a tighter temperature range.