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**Introduction:** Polyester Batting and Polyester Fleece are two popular types of insulation for clothing and sleeping bags. Fleece is a stronger material but holds less air, so is convenient for stitching garments, whereas batting is more suitable as a filling for sleeping bags, combined with a stitched cover. We would expect that batting is a better insulator because it traps more air. Let's see.

**Method:** I took two flasks of boiling water ( 0.5 kg water ) and wrapped one with batting and the other with fleece. I waited one hour and measured the temperature. I repeated the experiment twice to avoid errors. Here are the results:

Batting ( Exp 1 ) | Fleece ( Exp 1 ) | Batting ( Exp 2 ) | Fleece ( Exp 2 ) | |

Area Density ( kg / m2 ) | 0.283 | 0.192 | 0.281 | 0.198 |

Temperature Loss ( Kelvin per hour from boiling ) | 20 | 29 | 21 | 26 |

Insulation Value ( Inverse of Previous Row, Proxy for R value ) | 0.050 | 0.034 | 0.047 | 0.038 |

Insulation Value per Area Density | 0.176 | 0.177 | 0.167 | 0.191 |

**Conclusion:** Temperature loss is proportional to the energy lost by the material and is inversely related to the R value of the material. According to this quick experiment, batting and fleece are almost the same. So fleece, with its other advantages, is the winner.