I got the chance to play around with all of them, here are my comments for each of the packs:
pack A: Silicone or EPDM. The most ordered pack. It has a very small key travel reduction, so you may or may not notice it. It dampens the noise pretty well, and eliminates almost all of the “shock” you feel when the key hits the bottom. If you can’t decide which pack to get, try these ones first. Can’t go wrong with these ones, they’re good all around. I’ll be using pack A as a point of reference when comparing with other packs.
pack B: EPDM. These are nearly the same as pack A. Size is identical, but just a tad harder, which can only be felt if you pay very close attention. Otherwise if you mix and match the whole keyboard randomly with pack A and B, you most likely won’t be able to tell which is A or B. Noise dampening is the same as pack A, only difference is the hardness felt when keys hit the bottom. These should have been the same price as pack A, but only reason why it’s more expensive is because I asked for this option after I already got a quote for pack A. I don’t feel there is a large enough difference to justify this as another option based on price and characteristics, so these will be dropped in the next round. Just get pack A if you want something like this one.
pack C: EPDM. There is a noticeable key travel reduction with these, but that’s what it’s meant to do. Thickness is essentially in between pack A and E, so good if you want something thicker than A, but feel that E is too thick. I personally had a hard time deciding to use pack C or E. Otherwise, shock absorption and noise dampening is the same as pack A.
pack D: EPDM. I should rename this to “useless” pack. 1mm thickness is too thin. So although it did nothing to key travel reduction, it also didn’t do anything to noise dampening. The only time I can see this option being useful is if you bought some SP caps with short stems where these will make a difference. I don’t have a full set of SP caps, so I can’t comment on how useful it will be on those caps. However for stock caps and PBT caps from KBC, these had no effect. They will also be dropped in the next round.
pack E: Silicone or EPDM. This one is my personal favorite, but I know it’s not for everyone. It’s the max thickness you can have in an O-ring. It bottoms out just after the key’s registration point. This simulates scissor switches on laptops or thin membrane keyboard, but still retains the “mechanical” feel from MX switches. The main purpose of this pack is to reduce the key travel, but if this is not what you’re looking for, then get pack A.
pack F: Nitrile. Same size has pack A, but noticeable harder. These are only for people that think pack A is too soft or want to retain as much of the bottom out feeling as possible. It will still dampen most of the “clack” noise when the keys hit the bottom, but not as well as pack A. They feel great on PCB mounted switches since there is almost no change in the “natural” feel of bottoming out on the PCB.
pack G: Nitrile. These are the exact opposite from pack A, it’s different in size and softness. It’s essentially pack E, but harder. They’re for those that want a max key travel reduction crips bottom outs, and some noise reduction.
pack H: Silicone. This pack is the most interesting of all of them. It’s the softest feel of all of them and only comes in silicone because the other materials can’t reach this level of softness. These are a tad thinner than A, B, or F, which is what gives it the unique characteristics. Under normal typing conditions, it will eliminate most noise and shocks. However, because of the exact thickness of it, combined with its extra softness, it will feel like there’s no O-ring at all if you hit the keys very hard. This sort of gives the whole keyboard a dampening “film” effect, where the shock and noise dampening properties are there, but thin enough so there are no key travel reduction.