I love nylon string as main paired with soft poly as cross, its charactheristic is the best for me.
After more than a week hadn't played tennis I just realized the main problem for this kind of hybrid is the sawing effect even before it snap off. Today my nylon (Red Alert 16) was still in good condition but severely sawn, that made the cross locked-in. It greatly affected spin production and comfort while the power was still there (flat strokes like volley, serve and smash aren't affected much).
Makes me wondering what is the best nylon/multi for sawn resistant? Or is there any technique that can greatly help reducing the sawn effect? (I had lubricated the string but not helping much)
Yes, nylon or multi mains play well with poly crosses, but the mains are quickly sawn and soon break if you play with much spin and/or string loose. Nylon (and multis,and remember that multis are just many strands of nylon stuck together with an elastic glue of some kind, like polyurethane) has a tendency to cut very easily when under tension. This is well-known in the rock climbing community, because braided nylon ropes are used for safety during a climb because they are strong and elastic (they soften the impact of a fall because they stretch). They are also very abrasion resistant. It's not easy to cut a nylon climbing rope with a knife. But, if you put the same rope under tension you can cut it very easily.
The same thing happens with nylon strings, which are obviously under tension when strung in a tennis racquet.
In addition, the friction at the string intersections can generate a lot of heat if you hit with spin - in which case your strings are sliding and snapping back on each shot. All that movement and friction produces so much heat that the nylon strings will actually melt at the intersections, creating notches.
Why don't poly strings do this as much or as fast? Because they are 1) Hard. Not the same thing as stiffness. The surface of copoly strings are hard and difficult to dent with a sharp object. Nylon strings have low surface hardness and it is easy to dent them. 2) Slippery. Copoly strings tend to have very slippery surfaces, while nylon strings are "gummy" and sticky in comparison.
So how do you prevent a nylon string from getting notched or cut and then breaking? You could make it harder, and some manufacturers have tried, but if you put a hard coating on a nylon string that coating is usually less flexible (more stiff) than the nylon underneath. Since we like nylon strings because they are less stiff than copoly this isn't a good solution. Plus, coatings are not very thick and tend to wear off.
You could also try to make nylon strings more slippery. Several manufacturers have made nylon or multi strings with slippery coatings (Babolat Addiction, Yonex 850 Pro, Babolat Nvy, etc.) but these are usually too thin to withstand the sawing action in the mains for very long. They excel as crosses, where the friction and heat is spread out over an inch of string surface rather than concentrated at the intersection, but they are barely better than normal syngut as a main string.
Prince wrapped a nylon string in PTFE (like Teflon) and made Recoil. PTFE has a lower coefficient of friction than copolys and the strings slid and snapped back just like copoly strings. But in the mains they still got sawed and eventually broke because of low surface hardness. They would dent and eventually get notched. Once the PTFE surface was cut the nylon underneath would get sawn just as quickly as any other nylon string and then the string would break.
Maybe the most promising approach is to apply a lubricant to nylon mains. Even if your strings are deeply notched, applying a lubricant will reduce interstring friction, increase spin through the snapback mechanism, and to some extent reduce heat buildup (because of reduced friction) and thereby slow down the notching process. But lubricants are messy and must be regularly reapplied. They are not very popular.
Natural gut is a much better choice as mains paired with copoly crosses, for two reasons. 1) Although they are not hard, they do not melt like nylon (a plastic) and so do not notch in quite the same way. 2) The Tennis Warehouse University Professor thinks that natural gut may release natural oils from inside the strings onto the intersections as notches begin to form. This would be much like applying a lubricant, but without the hassle of doing so. So you have a self-lubricating string that doesn't melt. It's also much more elastic than nylon and so returns more energy to the ball. So you get consistently excellent spin, good durability, and good power. It also lasts much longer for me with copoly crosses than nylon mains do.
I'll lubricate my string from day 1 then.
