Inside a cover is better too, so there is much less airflow, which keeps it fresh and reduces the chance of it drying out. I believe its safer to use a proper table tennis cleaner as we can be confident that these will have no detrimental effect on the rubber. Next time you play you can just pull the plastic sheet and you're ready to play. You should cut it to the shape of your rubber, but slightly bigger. There are many other cleaners out there that people use, but the long-term effect of these is often unknown or not documented, so better safe than sorry.NOTE: If you have not cleaned the rubber for a long time, you may need a proper rubber cleaner (like the special rubber cleaner foam sold in tins specifically for table tennis) to clean the surface. Then apply the plastic protection sheet (make sure they are clean too!), pushing it on firmly, and pushing out any big bubbles so that the plastic makes contact with the rubbers everywhere (very small bubbles will be to hard to get out, but this does not matter).
One nice aspect of most Chinese style table tennis rubbers is their tacky or sticky surface, which is great for generating spin. Make sure it's kept out of the sun or very hot areas as this can damage the rubber. Just make sure there are no chemicals on there that could harm the rubber, and that it's rigid enough so that it does not tear when you pull it off the rubber. The common kitchen sink sponges are often too abrasive, which can damage the delicate surface of the rubber very easily.The simple procedure does not only protect the rubber and keep it tacky, but for many rubbers it will make it tackier over time.
The downside of this is that it attracts dust and dirt, which sticks to it making the rubber patchy and inconsistent. It needs to be soft & moist enough so that it does not scrape the surface of the rubber.So how do you use these two things to look after the rubber? Well every time after you finish playing, you need to rub all the dust off the surface of the rubber. Use the sponge or cloth, damp with water, to completely clean the surface. After cleaning wait for it to dry completely (important!).Firstly you need to either keep the plastic protection films that came with the rubber, or you need to buy/make some.
There are some sponges specifically for table tennis, but other ones can be used as well.Secondly you need a lint-free cloth Air Shower Suppliers or a sponge to clean the rubber with. Distilled water is the best, but I found filtered water or even tap water works ok.After you have applied the plastic protection sheets, put your bat away preferable inside a cover. There are some made specifically for table tennis rubber, or you can use sheets like those used in overhead transparencies. This guide offers some simple tips on how to keep you rubber clean and tacky, making it much better to play with, and prolonging the life of the rubber. Make sure cloth/sponge is damp enough not to scrape the surface of the rubber, but not too wet as to get the rubber soaking wet.