All thermal aluminum windows manufactured by J&M Glass pass very strict industry specifications. That alone makes them a good choice, but there’s more. According to one of the specifications, air leakage cannot increase more than 0.375 cubic feet per minute (CFM) for each foot of weather-stripped window boundary with a 25 MPH wind raging outside. Our 700 Series Double Hung permits only 0.06 CFM air percolation and that is only one sixth of the industry standard specifications!