shock cord

I am a bit confused about shock cord. I am looking for a source and ebay rope looks like bunge rope. The cord on my bags looks like rope but seems to compress. Almost as if the core had space. It is not 550. Can some explain to me the differences and what you guys use?

It's basically a small diameter bungee cord.

http://www.diygearsupply.com/cgi-bin/shelf.cgi?numb=57

REI has several different diameters and that is where I got mine. There are also several cottage industries that can supply your needs. Hope this helps.

For a cheap source of shock cord go to your nearest Harbor Frieght and get a cargo net @ around $5.00. Takes a little work to unknot it but you end up with 100' of 1/8" shock cord.

The Harbor Freight cargo net works but it only has about half the stretch of the shock cord I got from DIYgear. I have the cargo net cord for trying out ideas but I'd recommend getting the good stuff from a vendor here if you're going to the effort of making gear.