Every theme available, free or premium, will work with bbPress because bbPress is made to work with any theme through the theme compatibility layer.
bbPress is made to work with any theme, and in most cases, it will look the same with every theme. Still, bbPress styling and templates can be fully customized, and here are the 5 best looking premium themes that vastly improve how bbPress looks like.
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All prices are subject to change, and for the latest price, check the theme websites.
Forum is a great looking theme that features mostly styling based customizations to the bbPress, but with really great results.
OneSocial is a clean theme with very neatly designed bbPress layouts. bbPress templates are spacious and really look great. Theme is mostly changing bbPress styling, while templates are not modified. Theme has full BuddyPress support, and it is a great choice for any sort of forum or community based website.
Foro is one of the best looking bbPress themes available, and unlike many other themes, this one relies on own custom templates for bbPress to modify the layouts for some parts of the forum.
Boss is more of a community-oriented theme, build for BuddyPress first, but with some very nice looking bbPress styling. Theme is mostly changing bbPress styling, while templates are not modified.
Disputo is the very nice looking theme, made with the forum in mind, and there are a lot of customizations made to templates and styling as well. But, some of the changes made to templates, can cause some problems with styling that works with default templates, and will not work here.