# String Theory: Hollow Strings?

#### Gmedlo

##### Professional
Maybe the answer to simulating gut (or find something better) isn't to use more fibres/filaments, but to use none at all. Has an air-filled string ever been created?

Think about it, you could take a stiff poly, thicken out the gauge a little, and have 20% of the middle filled with air. I think this would drastically lower the stiffness, not to mention it would impart a great pocketing feel. You would also get more power as the string not only rebounds from its position on the racquet but the air filling the space from the depression of the ball.

Polyester itself is stiff enough that the air tunnel throughout the string wouldn't collapse either, even when you cut one end.

I probably sound like a nut.

#### lethalfang

##### Professional
Maybe the answer to simulating gut (or find something better) isn't to use more fibres/filaments, but to use none at all. Has an air-filled string ever been created?

Think about it, you could take a stiff poly, thicken out the gauge a little, and have 20% of the middle filled with air. I think this would drastically lower the stiffness, not to mention it would impart a great pocketing feel. You would also get more power as the string not only rebounds from its position on the racquet but the air filling the space from the depression of the ball.

Polyester itself is stiff enough that the air tunnel throughout the string wouldn't collapse either, even when you cut one end.

I probably sound like a nut.
If I assume all the fibers in a multifilament string is cylindrical, and I assume there is no filling between the fibers, then there is already a 10% volume occupied by air, due to the fact that you cannot pack circles (or cylinders, or spheres) around each other without creating space.
If you simply "poke a hole" in the middle of a string, then when the string is stretched, the "hole" will collapse.

##### Semi-Pro
Maybe the answer to simulating gut (or find something better) isn't to use more fibres/filaments, but to use none at all. Has an air-filled string ever been created?
Very impressive thinking. Looks like Babolat had almost the same idea with Xcel multifilament string:

“Includes Air Jet Technology, which encases every single fiber (1,152) by an injection process of a new patented material (a reformulation of polyurethane), which injects and releases air as the string moves.”

http://www.tennis-warehouse.com/descpageACBAB-BXCEL17.html

#### Nuke

##### Hall of Fame
I remember there was a nylon oil-filled string when I was younger that sounds like your idea, but with oil filling the hollow void instead of air. That might work, and the oil would keep the void from collapsing.

#### Gmedlo

##### Professional
If I assume all the fibers in a multifilament string is cylindrical, and I assume there is no filling between the fibers, then there is already a 10% volume occupied by air, due to the fact that you cannot pack circles (or cylinders, or spheres) around each other without creating space.
If you simply "poke a hole" in the middle of a string, then when the string is stretched, the "hole" will collapse.
If the hole is constructed along with the string, instead of after the strings composition has settled (poking), then the hole shouldn't collapse. I tried this with some copper wire coating– When tensioned on a machine, the hole is still their, shrunk in proportion to the stretching of the string.

Edit: sorry for double post.

#### gjoc

##### Semi-Pro
Dang, I thought I could make money off this :sad:
I wouldn’t say you should give up--you may be onto something.

Just because you’re not the very first doesn’t mean you can’t still pursue your idea.

That somebody else is thinking along the same lines may actually be a good indication that you’re on the right track!

#### lethalfang

##### Professional
I remember there was a nylon oil-filled string when I was younger that sounds like your idea, but with oil filling the hollow void instead of air. That might work, and the oil would keep the void from collapsing.
I had some Gosen Signal strings. There're metal corks on the two ends. When I cut the strings, oil leaked out. I was wondering why the heck they put oil in the strings.

#### ChocolatePie

##### Semi-Pro
It sounds like something that might break easily though.

#### Gmedlo

##### Professional
It sounds like something that might break easily though.
If the strings were made using polyester I don't really see an issue with durability, as it would still probably be more durable than basic syngut.

The real trouble would be the manufacturing proccess... still gotta find out how I would make hollow polyester string

#### iplaybetter

##### Hall of Fame
it would have to have some form of pressure so that the clamps don't kill it, but it must remain string able

#### User Name

##### Semi-Pro
this is a really cool idea. id really like to know how it could play. having the air cushening with the durability of a poly... anyone have an old spinning wheel?

I think that the way to do it would be to build the string around a wire. The wire would need to be thin to maintain a decent gauge. probably if you had liquid polyester, you could dip the wire in it to give it a coating. Then, pull out the wire to test it *once dried*

#### User Name

##### Semi-Pro
oh by the way, did neone notice that the second patent for the hollow air string was recent, 2007

#### Bent

##### Semi-Pro
In the recent years I played with Gosen oil filled 1,40 mm string.

It lasted forever and palyed terribly.

It was some kind of leftover I got and app. 20 yrs. old.