Thermarest Boost 650 (-6C, down)
Ultralight comfort meets customizable warmth with the Boost 650—designed for warmer-weather backpacking with the freedom to adjust shape, temperature, and fit. Its roomy semi-rectangular design lets you sprawl or side sleep, while the unique WarmZip™ center zipper pulls the bag in to boost warmth by up to 6°C, mimicking a mummy shape when needed.
Multi-use arm holes let you reach out, read, or regulate heat without leaving your bag, and a two-way side zip offers versatile ventilation. Plush 650-Fill Duck PFAS-Free Hydrophobic Down is zoned for maximum thermal efficiency, and the soft-touch, 100% recycled shell and liner are PFAS-free and eco-conscious. Thoughtful details—anti-snag YKK zippers, cinchable hood, draft collar and tube—round out this feature-packed, backpacking-ready bag. Available in multiple sizes and widths for the perfect fit.
| Regular | Regular Wide | Long | Long Wide | |
| Insulation: | 650 Duck Down | 650 Duck Down | 650 Duck Down | 650 Duck Down |
| Warmth rating: | -6C (20F) | -6C (20F) | -6C (20F) | -6C (20F) |
| Weight: | 1205g (2lb 11oz) | 1515g (3lb 5oz) | 1398g (3lb 1oz) | 1737g (3lb 13oz) |
| Stuffed size: | 32 x 19cm (12.5 x 7.5") | 34 x 19cm (13.5 x 7.5") | 33 x 19cm (13 x 7.5") | 37 x 19cm (14.5 x 7.5") |
| Inside length: | 183cm (72") | 183cm (72") | 198cm (78") | 198cm (78") |