These procedures are applicable to paper modified with polystyrene. Two alternative methods can be used: ultraviolet and gravimetric.These can be used for products covering a wide range of polystyrene content. The UV method is more sensitive than the gravimetric method and can be used for determining very low polystyrene loadings as low as 0.1%. The practical lower limit of the gravimetric method is approximately 1% polystyrene content.