What kind of string to use for the ice fishing experiment for kids? Classic ice fishing experiment for kids.

I used nylon because I saw it in a stationery, and apparently that doesn't work because I guess it's too slippery. I tried thread from my mom's sewing kit, but that doesn't work either.

I'm not sure I can find yarn or kite string in the stationery or nearby so please suggest alternatives expected to be found in the average household, supermarket, grocery store or convenience store.

Also how long should we wait? The above video takes only 10 seconds while this video takes about 2 minutes (off screen). What factors influence waiting time? Amount of salt? Type of string?
This resource has an explaination of the behavior, which relies on the salt-dissolved water wicking into the string. This would mean that you need a type of string which will absorb water. It's surprising to me that your nylon string doesn't work (as long as it's thick/low-density enough to absorb water, probably unlike fishing line), is it possible it has a hydrophobic coating? 

I would recommend any cotton-based string or twine. Cooking twine and sewing thread is often cotton, if you have access to that. I've had no problems with these. 

Edit: I just thought, that you might want to try this not in a cup of water first (like in the link above). You might potentially run into not-string-related problems if your water isn't cold enough, or if your ice gets too submerged when you put the salt on it. It's possible your nylon string is fine.