Sleeping bag liner SEA TO SUMMIT Reactor Midweight L - beluga

SEA TO SUMMIT Reactor Midweight L - beluga is a sleeping bag liner engineered to increase thermal performance and hygiene inside compatible sleeping bags. Made from insulating, lightweight materials, the midweight Reactor liner provides an extra warmth layer without significantly increasing bulk or pack size. The L size accommodates larger or long sleeping bags and users who prefer more interior space. The neutral beluga colour offers unobtrusive styling for outdoor and travel use.

Advantages

The Reactor Midweight L enhances overall warmth by adding an insulating layer between the sleeper and the main sleeping bag, helping extend its usable temperature range. Constructed to be lightweight and compressible, the liner packs small for backpacking and travel. It also acts as a hygiene barrier that is easier to wash than a full sleeping bag, and it is designed for compatibility with a wide range of sleeping bag shapes and zippers.

Suitable for

• Backpacking trips where lightweight additional warmth is required
• Car camping and multi-night trips to protect sleeping bags from sweat and dirt
• Cold-weather travel where a midweight thermal boost is needed without a heavier bag
• Tall or larger users who need an L-size liner for better fit

When it may not be suitable

The Reactor Midweight L is not intended to replace a purpose-built cold-weather sleeping bag; it is an insulating liner designed to supplement warmth rather than provide standalone extreme cold protection. Users requiring maximal thermal performance in sub-zero conditions should rely on a suitable sleeping bag rated for those temperatures rather than only a liner.

Key specifications

• Insulation level: midweight thermal boost
• Size: L (sized for larger or long sleeping bags)
• Colour: beluga
• Weight: lightweight and packable construction
• Compressibility: designed to pack small for travel and backpacking

How to use

Place the Reactor Midweight L inside a compatible sleeping bag so that the liner lies flat against the interior shell. Align the liner with the sleeping bag’s zipper and footbox area to ensure full coverage; some sleeping bags allow attachment using internal loops or by tucking the liner in place. Use the liner alone in mild conditions for added hygiene or combine it with a sleeping bag to increase warmth. After use, air out the liner and follow the manufacturer’s washing instructions to maintain insulation and hygiene.

What to consider before purchase

• Compatibility with your sleeping bag shape and zipper configuration
• Whether a midweight insulation level provides the thermal boost you need for your typical conditions
• Size requirements — choose L for larger or long sleeping bags and taller users
• Care and washing needs to maintain hygiene and insulation performance

Usage recommendations

For best results, combine the Reactor Midweight L with a sleeping bag whose temperature rating is close to your expected conditions; the liner will raise comfort and warmth without significantly increasing pack weight. Pack the liner in a compression sack when backpacking and launder according to care instructions between extended trips.