The vinyl mainframes of APCO Windows are filled with patented R-Core insulation (pre-expanded high-density solid-polyurethane), the same type used in many refrigerator/freezer doors. It prevents voids and settling, resulting in even distribution for the maximum insulating barrier.
U.S. Patent Number: 4,516,356
*Ply Gem Contractor, Pro or Premiums Series windows only. Offer is for HPMax triple pane glass. Valid only for homeowner replacement customers who purchase APCO products for their own residence and have them installed by APCO. Not valid with any other offer or promotion. Prior sales excluded. Offer not valid when purchasing three (3) or less windows. APCO reserves the right to terminate this promotion at any time. Other restrictions may apply.