To summarize some of the reasons why we believe this, and you can look at Page 4 of the slides, about 90% of our net sales are generated by proprietary products, and around 3/4 of our net sales come from products for which we are the sole source provider. About 60% of our revenue and a much higher percent of our EBITDA comes from aftermarket sales. Aftermarket revenues have historically produced a higher gross margin and have provided relative stability in the downturns.
Because of our uniquely high EBITDA margins, typically about 50% of revenues and relatively low capital expenditure requirements, typically less than 2% of revenue, TransDigm's year in, year out generated very strong free cash flow. We pay close attention to our capital structure and view it as another means to create shareholder value. As you know, we have in the past and continue to be willing to lever up when we either see good opportunities or view our leverage as sub-optimum for value creation. We typically begin to delever pretty quickly.
We have a well-proven, value-based operating strategy focused around what we refer to as our 3 value drivers: new business development, continual cost improvement and value-based pricing. We stick to these concepts as the core of our operating management methods. This consistent approach has worked for us through up and down markets and has allowed us to continually improve and increase the intrinsic value of our business while steadily investing in new business and platform positions.
We have also been successful in regularly acquiring and integrating businesses. We acquire proprietary aerospace businesses with significant aftermarket content. We've been able to acquire and improve proprietary aerospace businesses through all phases in the cycle. Through our consistent focus on our operating value drivers, a very clear acquisition strategy and close attention to our capital structure, we have been able to create intrinsic value for our shareholders for many years through up and down markets.