The lightweight Sea to Summit Ultra-Sil Compression Sack compresses your clothing and gear to around 1/3 the volume, saving space in your pack.
Sea to Summit says:
If you need to compress down your gear into the smallest possible space while adding minimal weight, pack it into Siliconized CORDURA® Brand fabric Compression Sacks.
The Sea to Summit's Ultra-Sil Compression Sack is ideal for compressing your gear while keeping the contents secure. The 4 extra long straps allow it to be filled to capacity, then compressed to maintain it's pack size which is roughly around the size of a soft drink can.
The Ultra-Sil Compression Sack is roughly half the weight of the original Sea to Summit Compression Sack so its ideal for those who want to save a little more weight.