CDN is a mechanism where a network of multiple servers at different places caches all your website static content like images, CSS, Javascript and stores it on their own servers. When a user visits your site, then instead of loading such content from your hosting servers it loads it from the CDN servers which increase the performance and security of your website and also saves bandwidth
CloudFlare
CloudFlare is the most popular free CDN service which you can use for your WordPress site to secure and speed up your site with ease. As CloudFlare blocks suspicious threats and limits access for potential abusers, it will also make your website more secure. To use their services you just need to create an account in their website and add your site. Once your site is added, you will get a custom name server for your site. Now just update your website’s original nameservers with the provided ones. You can also use their free plugin with ease.
Photon
Photon is a CDN service for those who have hosted their site on WordPress.com. However, if you have self-hosted WordPress sites then it is just a part of Jetpack plugin. Text and images are the two essential parts of any website, but images are the heavy components of web sites that take the maximum time to load. So, if you are using Photon then all your images will be served through WordPress.com, which reduce the loading time of your site to a huge extent. The good thing is that Jetpack is a free plugin and so is Photon service.
jsDelivr
Every WordPress site uses JavaScript some or the other way and also the theme and plugin used in Wordpress are used in JavaScript. When you open your website, these JavaScripts have to be run which might decrease the speed of your site. So, jsDelivr free CDN service is a custom service to host JavaScripts of your site to speed up the loading process of your website. To activate this CDN service you just need to install a free plugin of jsDelivr.
Swarm (Swarmify)
This service is relatively new compared to the others in the list, but it offers a free plan with 250 GB of free transfer. SwarmCDN is a relatively new peer-to-peer based content delivery network. They offer you pay as you go service which is really good for growing websites, and you get 30 days free trial for their paid package. Its features include hive caching, lazy loading, predictive loading and more. It is available in 196 countries worldwide.
Incapsula
Incapsula CDN service is another well-known CDN service that offers both free and paid plans. It routes your entire website’s traffic through their globally distributed network of high-end servers to give you spam protection service to protect your site from spam bots, access control, login protection etc for free. Use their WordPress plugin that will help you to get correct IP Address information for comments posted to your site. In a nutshell, it provides Global CDN, Website Security, DDoS Protection, Load Balancing & Failover protection.
CorelCDN
CoralCDN is a project from the MIT which is a peer-to-peer based content delivery network and it is absolutely free of cost. P2P networks rely on the billions of computers connected across the Internet which is mainly why CoralCDN is free. The way Coral CDN works is by serving the static content through their servers by appending ‘nyud.net’ to the URL.’
CDN.net
CDN.net offers you 1 TB free CDN bandwidth which is enough for a website with moderate traffic and images. CDN.net is a pay-as-you-go content delivery network that offers services worldwide. CDN.net makes your content secure and easy to access by providing users with DNS infrastructure, edge servers, DDoS protection, a mobile-ready control panel, and more. It hosts content in 113 cities in 43 countries to improve web performance for the regional, national, or international audience.