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SIDING INSULATION

XPS vs EPS

Test data and side-by-side performance: extruded polystyrene (XPS) vs. expanded polystyrene (EPS) as siding insulation.

As seen in the Milwaukee Area

Test Data Proves XPS Insulation Delivers on Every Key Factor

When choosing insulation that goes behind your siding, the difference between extruded polystyrene (XPS) and expanded polystyrene (EPS) shows up in density, R-value, compressive strength, water-vapor permeance, and moisture resistance. Here’s how the numbers compare.

XPS Advantage #1

Higher Density

77% more density

  • The greater the moisture resistance
  • The tighter the structure (closed-cell)
  • The higher the R-value, the greater the resistance to heat flow
  • One cubic inch of Styrofoam XPS contains millions of tiny cells
  • Unique closed-cell structure helps block transfer of heat and cold
  • Provides maximum energy savings
XPS Advantage #2

Higher Compressive Strength

250% higher compressive resistance

  • Compressive Resistance — the amount of force needed to deform the XPS insulation
  • The higher the compressive strength, the harder it is to damage the insulation
  • A higher compressive strength helps keep walls more uniform and straight when placed over existing siding
XPS Advantage #3

Water Vapor Permeance

Effectively handles water vapor permeance

  • Water Vapor Permeance — the amount of water in the vapor state that passes through a product or system
  • EPS insulation has a 5.0 perm rating
  • Vinyl siding has a 0.05 perm rating
  • When a substrate is laminated (such as EPS and vinyl siding), it takes on the properties of the lower of the two — the 0.05 perm of vinyl siding
  • Dow 3/4" T&G XPS insulation has a perm of 1.1 — it will not trap vapor moisture
  • Dow XPS is not attached to the siding so it does not take on the 0.05 perm
  • By maintaining its consistent perm rating, Dow XPS allows harmful moisture to escape the home
  • Dow XPS creates an effective drainage plane, allowing rain and wind-driven water to escape quickly through siding weep holes
XPS Advantage #4

Superior Moisture Resistance

Lower water absorption + retained R-value

  • Water Absorption — the volume of a liquid that becomes trapped in a product
  • 3/4" XPS takes on 0.1% water vs. EPS at 4.0%
  • For every 1% moisture absorption, you lose 5% of the R-value
  • If the R-value of 3/4" of Type I EPS = 2.7 per inch, it will reduce to 2.16 after taking on 4.0% moisture
  • Wet insulation loses thermal integrity and facilitates energy loss

Buy it right the First Time.

Most homeowners overpay because no one diagnosed the real problem first. Let’s fix that.

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