Insulation is rated by R value. The higher the number, the more effective it is in stopping unconditioned air from entering into your home or heated air from leaving your home.
If you have no insulation at all in your floor and you add R-19 you will experience a 90% improvement in reducing heat loss. If you already have R-19 and you upgrade to R-30 you will experience a 36% improvement after the upgrade. These statistics come from the Clark Public Utilities web site.
In Washington State the minimum R value in crawl space floor insulation for new homes is R-30. Many older homes that either donít have any floor insulation or their existing insulation is old and ineffective will experience a substantial improvement by adding R-19.