Ask 'Dr. Spa' Q & A Message Board

: The foam on the inside of the cover is sealed in polyethylene. Hopefully
: the polyethylene is heat sealed closed rather than taped. Over time,
: the off gassing of chemicals and ozone break down the polyethylene
: causing it to become porous. Steam and evaporating water then
: penetrate through the polyethylene.

: Polyethylene.... Polyethylene in itself is water proof. Kind of. The
: manufacturing process (detailed below) produces small
: "beads" of the material that are then compressed together
: into blocks. While the beads are water proof, moisture can penetrate
: in between the beads.

: To "dry out" a cover, you'd need to remove the polyethylene
: and put the foam in a protected area for 6 months to a year. It might
: dry out in that time. But then you'd need to properly reseal the foam
: in the polyethylene. We use a $20k machine for this sealing process.

: The Manufacturing Process of EPS foam

:

: Expanded Polystyrene, or EPS for short, is a lightweight, closed cell,
: rigid, plastic foam insulation material produced from solid beads of
: polystyrene. EPS's properties of low thermal conductivity, high
: compressive strength and excellent shock absorption properties make
: it an ideal material for many uses. Expansion is achieved
: by virtue of small amounts of pentane gas dissolved into the
: polystyrene base material during production. The gas expands under
: the action of heat, applied as steam, to form perfectly closed cells
: of EPS. These cells occupy approximately 40 times the volume of the
: original polystyrene bead. The EPS beads are then molded into
: appropriate forms suited to their application.

:
:

: There are 3 manufacturing stages to attain EPS foam blocks:
: Pre-expansion:

: Polystyrene granules (resin) are expanded by free exposure to steam to
: form larger beads, each consisting of a series of non-interconnecting
: cells.

: The raw material resin used to manufacture EPS is received in the form
: of small beads ranging from 0.5 to 1.3mm in diameter. These small
: beads are formulated and manufactured by the suppliers to contain a
: small percentage (4% - 5%) of the naturally occurring gas pentane.
: This gas is impregnated throughout the body of each small bead. The
: pre-expansion phase of manufacturing is simply the swelling of the
: small bead to almost 50 times its original size through the heating
: and rapid release of the gas from the bead during its glass
: transition phase.

: Conditioning:

: After expansion, the beads still contain small quantities of both
: condensed steam and pentane gas. As they cool, air gradually diffuses
: into the pores, replacing, in part, the other components. Most
: manufacturers run the finished beads through a dryer to remove any
: surface moisture. Then they're stored in large open storage bags for
: an aging process. Besides the steam and gas in the beads there are
: also areas of internal vacuum in the millions of cells created. This
: vacuum must be equalized to atmospheric pressure otherwise this
: delicate balance may result in the collapse, or implosion, of the
: bead. This process of aging the expanded beads allows the beads to
: fill back up with air and equalize. This aging can take from 12 hours
: to 48 hours, depending on the desired expanded density of the
: bead.After this process they're ready to be formed onto solid blocks
: of foam.

:

: Molding:

: The molding process involves taking the loose expanded beads and
: forming them into a solid block mass. A mold is filled with a
: specific amount of beads. A vacuum system evacuates any residual air
: from the mold. The vacuum is relieved by live steam which flows over
: the entire mass of beads in the cavity. This vacuum process softens
: the polymer structure of the bead surface and is immediately followed
: pressure compressing the beads and more live steam. The latent heat
: from the steam and subsequent pressure increase cause the beads to
: further expand. Since this is a confined environment, the only way
: the beads can expand is to fill up any voids between them causing the
: soft surfaces to fuse together into a polyhedral type solid
: structure. Pressure is released after a predetermined time and the
: loose beads are now fused into a solid block of foam. The density of
: the foam has been predetermined by the amount of pressure exerted on
: the beads while in the mold.

: Following a short cooling period, the molded block is removed from the
: machine, and after further curing and conditioning, may be cut or
: shaped as required using hot wire elements or other appropriate
: techniques.
:

Sounds like I've gotta start shopping for a new cover. Thanks guys!