What is patentable is a very complicated subject and there is no simple answer to what is patentable. That said, to be patentable, a new product or material must be more than an obvious extension of an existing an object or material, whether patented or unpatented. So, in your example, fingerless gloves are an obvious extention of "fingered gloves," obvious to anyone who pays any attention to apparel (e.g. you can analogize from short sleeved shirts, shorts, and any other clothing article which is a "shorter" version of another article). They would most likely not be patented.You cannot manufacture anything that is patented without the consent of the patent holder.Whether a given object or product is barred by some patent is also complicated, but the starting point to the analysis is the terms (the "disclosures") of the patent in question--you have to read the specific patent to see what it covers.