- Glass of early 20th century
- Virtually NO energy savings
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- Glass of the 1940's
- Better than single pane but still limited energy savings
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- Glass of the 1970's
- Higher energy savings but still lacks state-of-the-art insulation
- Very Heavy
- High rate of seal failure
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- Glass of the 1980's
- Higher energy savings
- Gives window a hazy look
- Prone to streaking
- Old Technology
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