3F UL Gear Tyvek Sleeping Bag Cover Liner – Waterproof Breathable Bivy (Type A & B)

Meet the 3F UL Gear Tyvek Sleeping Bag Cover Liner, a feather-light bivy-style liner designed to sit between your sleeping bag and the tent interior. Built with DuPont Tyvek, it blends waterproof protection with breathability to fend off dampness while letting your body heat and moisture vent outward. Its design is inspired by the idea of a bottomless bag: full foot closure keeps the feet cozy and prevents shifting, while the upper portion remains open for freedom of movement.

In real-world use, hikers and campers often face condensation and moisture inside tents, which can affect warmth and comfort. This liner aims to reduce interior moisture exposure and help maintain a more comfortable microclimate around your sleeping bag. Note that Tyvek's waterproofing and the liner's structure work best when used with a sleeping bag and a shelter such as a tent or tarp; it is not intended to replace a rain cover by itself.

Key benefits at a glance

• Lightweight protection: ultra-light materials keep pack weight down (Type A 130 g, Type B 200 g).
• Condensation management: designed to prevent dampness from entering the sleeping bag interior.
• Breathable waterproofing: Tyvek balances water resistance with ventilation to reduce moisture buildup.
• Easy packing and transport: compact pack size around 16 cm x 8.5 cm.
• Simple to use with your sleeping bag: full foot closure and open-top design for easy setup.

Size options

• Type A — 180 cm x 80 cm; weight approx. 130 g; compact when packed.
• Type B — 230 cm x 90 cm; weight approx. 200 g; additional length for larger bags or extra coverage.

Usage notes

• Use in conjunction with a sleeping bag; the liner's main job is condensation control inside the tent or bivy.
• Pair with a tent or tarp for best results; it is not a standalone rain protection solution.
• This item is an ultra-light liner; sleeping bag and other accessories are sold separately.

By choosing the Tyvek liner, you can enjoy a lightweight, tactile layer that helps you stay warm and dry on damp mornings or misty camps. It blends seamlessly into your camping setup, whether you are heading into a high-alpine night or a humid forest dawn. While results can vary with climate and shelter, many users report a more comfortable sleeping environment thanks to reduced interior moisture and improved heat retention during cold snaps.