Generally speaking the lower the tension the more power but less feel. The strings become like a trampoline and the ball explodes off the racquet. Of course if you string your racquet too loose your strings will move around a lot and this seems to really bother some people. How much does a strong out of place really affect your next shot? Properly negligible at best. An average squash tension is 27-28 pounds. I normally don't go more than 1 or 2 pounds higher or lower from this range, but it does make a big difference.
Another important thing to know about string tension is that factory strung racquets normally come strung quite high. The racquets normally have a 'ping' sound to them and I usually cut out the factory string. But I have the luxury of having my own stringing machine so it doesn't cost too much money. A racquet strung too high is dangerous for people that don't have proper and efficient swing biomechanics. If you have any elbow or shoulder issues you shouldn't get your racquet string too high. I would recommend 27 at the highest, or better yet some lessons to correct your stroke!
It's important to remember that string loosens up as you play with it. If you're a hard hitter or you don't break strings very often you may want to get the racquet strung a pound or 2 higher as it will slowly become your ideal tension.
Another important factor about string tension is the size of the racquet head. Mostly this has to do with the length of the main strings. The longer the main strings, for example on an open throat racquet I string the racquet a little higher. Whereas the old school, small head squash racquets had a small radius and could be strung at a lower tension, but would feel much tighter. Depending on the length of your main strings and also the number of them, you should increase or lower the tension accordingly. If you only have 12 main strings on anon throated racquet you are probably better stringing your racquet closer to 29 or 30 pounds. Unless of course you have a history of tennis elbow.
Different strings have different structural qualities and because of this they should also be strung at slightly different tensions. Ashaway Powernick 18 for example recommends striking their string 10% lower than other strings. Meanwhile Tecnifibre recommends stretching their string before stringing it, so again you don't have to string the racquet quite as tight as a racquet that didn't have a pre-stretched string.
Hardball doubles racquets are normally strung quite a bit higher. I don't get to play much doubles anymore, but when I did I would string my racquet at 40 pounds or even slightly higher. The ball is much harder than a softball and you will have too little control and your strings will move all over the place if you use a racquet string at 27 pounds. You will also find that you break a lot more strings playing with a hardball.
Types Of Strings
The main characteristics you are looking for in a squash string depend on your level, your style of play and the cost of the string. Most average club players could use any string and not notice much of a difference. For these players you want durability. For more advanced players who notice the difference in feel with their strings will be looking for a more advanced product. There are many on the market and I will cover the most popular ones now.
Supernick XLThis string has been around since I was a little kid. It's a good basic string. I find it has average durability and power with a low amount of feel. I recommend this string to any average club player who doesn't care much for the feel and wants to have a basic cheap set of strings. This string is a step above most cheap factory string, but I don't see many advanced players using it these days. There is also the Supernick Titanium which lasts sightly longer, but again has a low amount of feel.
This is one of the more popular choices I see at the club. This string is one of the best for overall durability, feel and power. It costs a little more than the basic Supernick, but is well worth the investment.
This string is similar the the above Powernick 18. It's the same gauge and made of the same material, but I would say has slightly more feel or touch. Some kids also just prefer blue string!
This string is not very popular from what I see in Canada, but I like this the best of all the Ashaway strings. It has a little more texture and feel to the string. The string is slightly thicker, but it doesn't really last any longer because of the texture. If you like to slice the ball and already use Powernick 18 or Ultranick 18, give this one a try.
X-One Biphase 1.18
This string has the most power of any Technifibre string. Because this string still has the same multifilament as the other classic green string it still has good feel to it. The durability is average, but pretty good for a Tecnifibre string. If you are looking for more power and don't want to loose your feel, give this one a try!
305 Gauge 17/ 1.20
This string is another top of the line choice. It doesn't have quite as much power with as the X-One, but has slightly more feel. This is a great choice for someone that likes to slice the ball.
305 Gauge 18/ 1.10
This string is the same as the one above, but is a thinner gauge. This is my string of choice. Because it is thinner, it is actually slightly lighter and I feel it has more tough. The only issue with this string is that is has poor durability. On average I break 1 set of strings per week, but I also have the luxury of owning a stringing machine. I only recommend this to 3 types of people. Those who have multiple racquets, as you need at least 3 to go to a tournament with. Those that have their own stringing machine (as it will get expensive). And finally those that are highly competitive and play at advanced level as you will notice the difference (because it's just the best!).
I know Tecnifibre has the 305+. I've only tried it once and I didn't care for it much. I haven't had enough experience with it to give a more thorough review.
I know there are lots of other companies that make string. There are probably even some very good products out there that I have never even heard of, but I cannot review them because I'm unfamiliar with the. If you want to ensure you are playing with a high quality string, try out an Ashaway or Tecnifibre model.
I'm always interested in hearing what types of string people like to use? Do you have another make or model that you really like? I'm always looks for suggestions. I'm not sponsored by any companies so there is no conflict of interest in any of my reviews.
Also, if you are a squash family and go through a lot of strings, you may want to invest in a squash stringer. My dad did when I was about 10 years old and I've strung well over a thousand racquets an still use the same stringer to this day. You can always start with a cheap tabletop stringer which should only cost a few hundred dollars. These tabletop string machines do the trick, but if you're doing a lot of stringing you'll eventually want something more study. If you do this, just makes you you don't start undercutting your squash club's string service. That's part of the way squash clubs and coaches make a living.
Play around with the types of string and the tension. You may just find something that suits your game better. If you're not sure what you're looking for, ask yourself what characteristics are you looking for in a string? Durability, power, control/feel, or just the colour?