The basic compound formula

The specific formulation in Flowing Table has 100 parts of raw gum elastomer and 160.15 parts of total material. After curing for 35 minutes at 140°C its vulcanized properties are indicated as 57 IRHD, with a tensile strength of 30 MPa and elongation at break of 645%. The specific formulation and properties are taken from 'The Natural Rubber Formulary and Property Index published by The Malaysian Rubber Producers Research Association (MRPRA) Rubber chemists use the term phr (parts per hundred rubber), meaning parts of any non rubbery material per hundred parts of raw gum elastomer (rubbery material). They prefer this rather than expressing an ingredient as a percentage of the total compound weight. Parts can mean any unit of weight (kg, lb, etc.) as long as the same weight unit is used throughout the formulation.

Specific Formulation
Material	PHR	For Example	PHR
Raw gum elastomer	100	SMR20	100
Sulfur	from 0 to 4	Sulfur	0.35
Zinc oxide	5	Zinc oxide	5
Stearic acid	2	Stearic acid	2
Accelerators	from 0.5 to 3	MBS	1.4
		TMTD	0.4
Antioxidant	from 1 to 3	HPPD	2
Filler	from 0 to 150	N330 Black	45
Plasticizer	from 0 to 150	Aromatic petroleum oil	4
Miscellaneous		None
		TOTAL	160.15
PHR is defined as parts by weight of ingredient per 100 parts of raw gum elastomer. The limits given are typical examples and are not intended to be absolute values.