While many players will have good intuition on choosing an appropriate mallet for a timpani part, it can be very helpful for a composer to specify what type of mallet they are looking for.
For extra attack, hard mallets are appropriate, though I’d recommend clarifying what sort of material you’d like to hear on the drums. Hard felt, chamois, and wood are all common and appropriate choices, but they sound very different. Keep in mind that hard mallets have uses beyond playing loud; they can be extremely useful to play articulate passages at a low volume, so consider specifying when that sound is desired.
Wood and chamois mallets are generally always hard, but there is a very large range in the characteristics of a felt mallet. Specifications such as Hard, Medium Hard, Medium, Medium Soft, and Soft are all very commonly used, though I personally am not a huge fan of Medium Hard and Medium Soft, as that to me is very vague. Choosing a type of mallet goes a long way in finding the ideal sound for a timpani part and is valuable information to maximize the effect of a piece.
Adam Holmes 