Hello!
In an ideal world, I would recommend looking at your analytics or interviewing customers to see how they interact with your site. Do they already know the exact product they're looking for? Or are they less familiar with the industry and in need of details and information on the over-arching category?
I personally like the idea of having a kind-of landing page for the product category – Solar Window Film – with some good quality content that answers frequently asked questions on the subject. From there, link to the individual products. This will help you rank for the more broad search term, while also allowing you to rank for the individual product.
As for whether or not to also display these as sub-nav items in your menu, I think you could do that as well if you like. To cater to the user who is already familiar and knows what they're looking for.
Hope that helps!