I was looking up pictures of the helmets and here is a Tipperary with the cover on it. Ew.
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Troxel Victory Show Helmet:
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This might be okay for dressage shows, the style is out of date for eventers and HJ (I think). I am not sure about dressage.


Troxel Grand Prix Classic Slim Profile Show Helmet
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This one looks like it will give you mushroom head BAD.

Troxel Legacy Gold Duratec
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I would say this one isn't showy enough for the dressage arena.


IRH Pro-Rider Gold
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Of all the basic velvet helmets, I think I like this one best, but I would prefer the harness in black.

IRH Olympian Velveteen DFS
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I think I like this one the least for a basic velvet helmet.


IRH Advance Tech
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I don't think this is going to be showy enough either.


IRH Elite
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I am not sure I like all the vents on this one. It looks a little tacky.

Charles Owen JR8
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Obviously my favorite.

Please if you are looking for a show helmet, get one that is going to be appropriate for shows and just get a nylon cover for it when you are schooling. If you get a not so appropriate show helmet and put one of the velvet covers on it, it looks cheap. Nothing bothers me more than somebody who has dressed nicely for the dressage arena, has a nice saddle and bridle, but a regular troxel with a velvet cover on it.

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Your best bet would be to look at a local horse show photogs website and see what is the style in your area for dressage shows. I would also talk to your trainer and fellow dressage riders.

In my area, at the local dressage schooling show there was more plain velvet show helmets than anything else, then came BLACK troxels, a varity or IRH helmets, one person with a velvet cover on a troxel, one person with a GPA and one person with a CO JR8 (ME!)

Whatever helmet you get, make sure it fits you correctly and the harness is snug against your chin. If it is kinda uncomfortable in the store, try a size up, if it still doesn't feel right, put it down. I made the mistake of thinking a slightly uncomfortable helmet would be more comfortable the more I wore it. A slightly snug helmet turned into a headache making machiene at shows when my hair was done for the show and when my head got hot.