K, I guess I ought to explain a little back story about kevlar cloth and how it relates to compositing...
(i.e. not under armor)
About Kevlar
What is it?
Aramid (Kevlar 49) is a low density, lightweight and extremely tough fabric. It was originally fabricated by DuPont.
Benefits
Kevlar is meant for things that need to be heat, flame, abrasion, and solvent resistant. So, it's generally used for brake pads, boathulls, and (what most ppl think) body armor. However, please note: 1 layer of Kevlar does not make something 'bulletproof'. Real bulletproof vests are made of
many layers of kevlar and a key component called the ballistics panel!
Cons
It is very difficult to cut and almost impossible to sand. To cut kevlar you need special scissors made for shearing it (expect to pay about $25). The actual kevlar is also expensive. The cheapest Kevlar cloth I find is about $22/yd (where Fiberglass cloth is about $5/yd). Also, for compositing,
kevlar is meant to be used with EPOXY resins. This
is not polyester resin which are the styrene based products commonly referred to as fiberglass resin or boat resin. ('Fiberglass resin' should also be noted as being cheaper and more common than epoxy resin.)
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So in relation to Mjolnir armor, yes, it can technically be done. Imo, it's a cool idea, however, it would be incredibly expensive and would have more frills than should ever be needed on the backing of costume armor.
My recommendation, on the inside, just use good ol' fiberglass

It's sturdy, easier, and more affordable. Lots of people here will attest to it and. And that way, you can use your creativity to spend that money on something that adds more visible appeal (aka "zazz"

) to your armor!
Just my 2 cents.
I hope that helps,

-Vex