Single or twin ply heads?
What difference do they make?  Will one type of head be more suitable for what I want?  Well this guide is intended to give some clues.  The information contained within is intended to be relevant to both toms and snare drums, so can applied to both.

Single ply heads.
Single ply heads can be used for either the batter or resonant side of the drums (although some single ply heads are designed specifically with the resonant side in mind).  When used as batter heads, they give the most open sound, with a degree of ring.  Tuned down, low and loose, they give a very fat tone, very punchy, while still retaining on open tone, and good volume.  Single ply heads, depending on the drums, can be most suitable for jazz, funk and pop, especially in situations without amplification.

Single ply heads would generally be used on the snare drum, more often than not the coated versions.  This is to allow the drum to “sing,” while the coating makes the sound a bit warmer.

Some of the best examples of single ply heads are Remo Ambassador/Diplomat (resonant), Evans G1/Resonant Glass, Aquarian Classic Clear (in clear, black or white).

Twin ply heads.
Twin ply heads focus the sound more, so are often preferred by drummers looking for that particular sound, most often for pop, rock or heavy playing.  They are also extremely effective in the studio, where a naturally focussed sound is desirable.

Twin ply heads often have an oily substance, or a substitute that creates a similar effect.  This “glues” the two plies of the head together so they respond with synchronicity when the head is struck.  Heavier versions of twin ply heads can be unsuitable in situations where playing live with no amplification, but when amplified, or in the studio, these heads can sound very round and deep.

Twin ply clear or coated heads can also be used on the snare if you are looking for a very focussed, almost dead sound, or if you are a very heavy hitter!

Good twin ply heads include: Remo Emperor/Pinstripe, Evans G2/Hydraulic, Aquarian Super 2/Performance 2.