For many years Grado had 3 types of cushion, the G, L, and S. The G was larger and bowl shaped, and came on the high end Statement headphones. The L was on most of the middle headphones, and the S was on entry models 60 and 80. The S was also known as the “comfy” cushion. The S is much like the flat on-ear pads of inexpensive headphones like box store Sony and Senn PX.
Grado has added the 2 part F cushion to many of the mid-range models. They can all be seen at the following official link. Other cushions are for specialty models.
The construction of the L and G cushions has been examined, and they appear to be of two densities of foam, with the more dense foam on the outside. The famous basic tape mod consists of putting tape around the outside of these cushions, creating a bit of a better seal and changing how sound reflects in the earpad.
The Yaxi cushions are like an improved S. Other manufacturers have additional designs. Most Grados can use any of the G, L, S, or F cushions.
Beautiful Audio has done quite a bit of work basing custom earpads on the G and L cushions, but increasing depth and providing choices of materials. They also have a kit to convert to a replaceable cable . When you order earpads, they suggest you measure your headphones - over the years there has been some small variability in Grado’s “ring size” for want of a better term, and they make sure the headphones fit. The website also goes into some depth regarding which earpads create which sound changes, much as the ZMF site does.
https://www.beautifulaudio.biz/grado-earpads-headbands
They now produce their own headphones also, but I’ve not heard any reviews.