Sea to Summit Ultra-SIL Compression Sack - Ultralight Pack Saver

In this review the Sea to Summit Ultra-SIL Compression Sack is evaluated for backpackers, frequent travelers, and anyone who needs to reduce bulky gear volume. The bottom line: it is an ultralight, well-built compression sack that reliably squashes clothing and sleeping bag liners down to free up real packing space. The review finds the 5-liter size best for clothing or small sleeping bag liners, and highlights the combination of lightweight bluesign-approved 30D Ultra-Sil Cordura nylon, a non-PFC DWR finish, and a thoughtful closure system as the single biggest reason to choose it.

Key Features

• Ultra-lightweight material: The 30D Ultra-Sil Cordura nylon keeps the sack extremely light at about 0.12 pounds, making it suitable for weight-conscious trips.
• Effective compression: Three compression straps compress bulky clothing and gear down by as much as two thirds to maximize space in a backpack or suitcase.
• Water-resistant finish: The non-PFC durable water repellent helps shed light moisture and keeps contents drier than untreated fabric.
• Secure closure and anti-tangle lid: An attached flip-top lid with a hidden drawcord prevents tangled straps and allows quick access to contents.
• Durability where it counts: Double-stitched seams and reinforced stress points plus a reinforced webbing pull handle at the round base improve long-term reliability.

Who It's For

The Ultra-SIL Compression Sack is ideal for backpackers, bikepackers, and minimalist travelers who need to save space without adding weight. It works well for compressing clothing, packable puffy jackets, or a light sleeping bag liner into a bottom compartment of a pack or in a carry-on.

It is less suited to users seeking fully waterproof dry sacks for prolonged wet conditions or those who need larger volume storage; buyers needing waterproof protection or larger capacities should consider other Sea to Summit models or purpose-built dry bags.

Pros & Cons

Pros

• Very light construction that trims pack weight while providing strong compression.
• Slippery Ultra-Sil fabric makes it easier to slide the sack into tight pack spaces.
• Reinforced seams and stress points provide confidence in durability for regular use.
• Attached lid and three-strap system produce even compression without strap tangles.

Cons

• Not a fully waterproof dry sack, so it will not protect contents in prolonged submersion or heavy rain.
• Some users may find the 5-liter size small for larger sleeping bags or bulkier items.

Specifications

Brand	Sea to Summit
Material	30D Ultra-Sil Cordura nylon (bluesign-approved)
Finish	Non-PFC DWR
Volume	5 liters
Dimensions	6 x 11.7 in
Weight	0.12 lb
Closure	Flip-top lid with drawcord and three compression straps

Our Verdict

The Sea to Summit Ultra-SIL Compression Sack is a smart pick for ultralight travelers who want reliable space savings without adding weight. Its combination of slippery, bluesign-approved fabric, reinforced construction, and an attached lid makes it a practical, durable pack accessory; those needing full waterproofing or larger volume should look elsewhere.

Frequently Asked Questions

Is this sack waterproof?
The sack is water-resistant due to the non-PFC DWR but not fully waterproof for submersion or extended exposure to heavy rain.

How much does the 5-liter size compress gear?
Customers report compression down to roughly one third the original volume for clothing and packable layers, with results varying by item.

Will it fit in a carry-on?
Yes, the 5-liter pack measures 6 x 11.7 in and is small enough to fit in the bottom of most carry-ons or the exterior pockets of backpacks.