First off, if you somehow missed the extensive post over on the site covering the Gen 1 Crye Precision Combats you need to check that out as both context for his post and for your general knowledge of gear evolution:
When I purchased the Gen 1 trousers the matching knee pads happened to be included, which was a stroke of luck to say the least as the sales listing did not specify which type of pads I’d be getting. Both the Gen 1 and 2 also look exactly the same when fitted. These are probably even rarer now than the G1 pants themselves and have actually been sold for higher prices on a couple of occasions.
The rubber-like outer cap is made of the same material as the far better known Gen 2 knee pads as far as I am able to tell, however the backing for that cap that fits inside of the knee pad pocket on the pants is the big difference here and as soon as you handle these pads it is actually quite obvious why Crye made the changes that they did for Generation 2.
The grey material shown in the pictures here is in fact a semi-rigid plastic which has had a thin layer of foam attached to its’ rear surface. The entire rear side is then tightly wrapped in a thin layer of black fabric, presumably some sort of nylon. The stitching between the tan cap and the grey plastic is as you would expect from later generations and the hook side velcro is slightly different in pattern but that’s a minor change and functions in essentially the same way.
The issue with these is that the grey plastic is already curved in one plain to fit around the wearers’ leg and the material doesn’t especially want to bend in the other direction as well. This means if you take a knee and the entire pad isn’t entirely horizontal and flat against the ground with the tan piece fully against said ground, the plastic can somewhat resist bending and an oddly shaped kink can form which isn’t necessarily ideal. The best analogy would be when you bend a cardboard tube and a crease is formed in one specific area.
As many of you will know if you’ve ever worn Crye combats (or similar) the pads will often end up riding a little high and your knee will only be resting on the foam of the lower part of the pad when in a kneeling stance, with the coloured outer cap not entirely on the ground. The change to an all-foam backing with Gen 2 addressed the aforementioned flexibility issue and the horizontal striations in the coloured cap of the Gen 3/Airflex pads deals with the positioning problem.
While these 1st gen pads would conceivably be quite a bit more resilient to puncture and sharply pointed objects by comparison to later generations (3 and 4 in particular) that advantage is not necessarily one that is of substantial use on frequent occasions to all users. The removal of the plastic in favour of all-foam construction makes a lot more sense and for most applications I would judge it to be the correct way forward. When we look at the multi-density foam and flexible cap construction of the Gen 4 pads there is a lot of iterative improvement to be seen. Although that said the fitment and outer silhouette of the pads has never changed and all generations of knee pad are compatible with all generations of combat pant and vice versa.