Kevlar all by itself will not make a really strong layup. It will be too flexible. It is advisable to add some glass or other material between layers of Kevlar. The outermost layer as glass is also a good idea as it handles abrasion better than Kevlar. 4 layers of material is probably the minimum. Areas that see impacts may benefit from more.

: I'm building an all composite sea kayak with kevlar as my main reinforcement
: material. I'm using 5 oz kevlar, how many layers are necessary for the
: hull? I've heard that it's strength is comparable to 6 oz fiberglass
: cloth, how many layers of that would I need? Is it necessary to cover the
: outside of the hull with glass to protect the kevlar and get a nicer
: finish? I was thinking I would use 4 layers of kevlar for the hull and 3
: for the deck, and maybe cover that with glass cloth if necessary. Would
: that layup be strong enough? Or is it necessary to use 5 or even 6 layers.
: Thanks
: Jake