650 Loft Ultra-Dry Down™ is used in the Sea to Summit Trek sleeping bags. 650+ Fill Power indicates that one ounce (30g) of down will re-expand to over 650 cubic inches after compression. This down provides an ideal warmth-to-weight ratio for the traveler, recreational camper, and occasional backpacker. The loft and down quality/composition are independently tested by the International Down and Feather Laboratory (IDFL) – a copy of the certification is supplied with every Sea to Summit sleeping bag.
The down is responsibly sourced and RDS certified and treated with the environmentally-friendly Ultra-Dry Down™ treatment.
All of which means you can rest easy.