NOVELTY - Foam process using low fugitive volatile organic compound emissions by using low permeability blowing agent(s) and a low volatility blowing agent(s).    USE - Used for foaming polystyrene, e.g. as a insulation board.    ADVANTAGE - Gives low fugitive volatile organic compound emissions. The foams also include nucleating agents which regulate cell formation and morphology.    DETAILED DESCRIPTION - A blowing agent for foaming polystyrene comprises essentially of: (i) at least one low permeability compound having permeability of lower than 1 x 10-12 cc (STP)(cm)/((sec)(cm2)(cmHg)); (ii) at least one low volatility compound having a b.pt. of higher than 23 degreesC and selected from acetone, acetone/water and/or methylacetate; and optionally (iii) at least one high volatility compound having a b.pt. of lower than 0 degreesC. The blowing agent comprises less than 70 wt.% of the low permeability compound. INDEPENDENT CLAIMS are also included for: (1) a polystyrene foam structure prepared by: (a) melting a mixture ocmprising a thermoplastic polymer; and (b) dissolving an effective amount of blowing agent in the mixture of step (a); (2) producing a polystyrene foam by using steps (a) and (b), and additionally steps: (c) forming an extrudate comprising 0.5 - 3 wt.% low permeability compound; (d) transferring the extrudate to an expansion zone; and (e) permitting the extrudate to expand in the expansion zone to produce the polystyrene foam having a density of 1 - 15 lb/ft2; (3) a blowing agent for foaming polystyrene, comprising a low permeability compound selected from cyclopentane, isopentane, isobutane, 2,2-dimethylbutane and/or cyclohexane; and (4) a blowing agent as claimed but the blowing agent comprising at least 15 wt.% of the low volatility compound.    DESCRIPTION OF DRAWING(S) - The figure is a schematic flow diagram of an overall sequence of operations in the manufacture of a foamed polystyrene sheet with the claimed blowing agents.    Hopper (11)    Primary extruder (13)    Point at which blowing agent is added (15)    Hollow adapter section (17)    Secondary tandem extruder) (19)    Annular die (21)    Bubble or tube (23)    Sizing drum (25)    Sheet stock (27)    Winding reels (29)    .