To a large extent, this whole rubber diaper theme is inspired by this post. (I highly recommend going there and reading the description and comments).

Here's what I wrote about it on e6ai (at the moment, this site has become my main platform for publishing):
Here is a pony in an unusual diaper, which is copied from real devices used on horses.
As you might guess, such diapers retain all secretions and do not absorb anything, but in addition, such a device can serve as a soft chastity belt, especially for mares. By the way, the illustration is most likely a mare. Another advantage of such diapers is the economic component - after emptying and washing, the rubber bag can be used an unlimited number of times.
In the case of intelligent mlp ponies, such a device may well prevent masturbation in mares, especially if there is a frame (skeleton) made of harder rubber stripes inside.
Compared to traditional, large, soft absorbent diapers, the rubber version looks really unusual. However, in the near future you can expect from me a different version of this image with an ordinary diaper.

Alternative version with a the ordinary diaper.

Also, if someone is interested in this information:
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Prompt: MLP feral white pony, wearing black rubber diaper, diaper cover, farm, stall, ponyplay, harness, bridle, black rubber diaper, white body, white fur, yellow mane, yellow hair, yellow tail, tail, wrapped tail, raised tail, hooves
Negative: boringe621fluffyrockv4, deformityv6, easynegative, bad-hands-5, bad anatomy, low quality, signature, logo, watermark, short legs, baby, latex suit, rubber suit, boots, socks
Size: 768x640 Sampler Steps: 20 CFG Scale: 8.00 Model: indigoFurryMixv120Hybrid Seed: -539261158

Upscale:

Size: 1536x1280 Sampler Steps: 15 CFG Scale: 8.00 Denoising Strength: 0.45 Seed: -264571055
```