A completely new version of this plugin is available and it allows to use the latest Polymer components: <a href="https://wordpress.org/plugins/wp-polymer/" rel="ugc">WP Polymer</a>
This plugin allows to add Polymer elements (v0.5) to your posts and pages, the same components used in Android Lollipop. You can use the HTML editor with the Polymer tags directly or the shortcode [poly] for all the elements. The correct HTML libraries will be loaded automatically. 
Polymer website: http://www.polymer-project.org/
Notice: Polymer is still in developer preview, some constructs may change in future. A modern browser is required to run Polymer web apps.
Features
<ul>
<li>Polymer tags directly available (core & paper) in posts / pages with the HTML editor;</li>
<li>[poly] shortcode to access all tags;</li>
<li>simple widget;</li>
<li>auto import the necessary HTML components;</li>
<li>code blocks to easily manage elements;</li>
<li>Javascript editor in posts / pages admin;</li>
<li>CSS editor in posts / pages admin;</li>
<li>import iconsets options;</li>
<li>autop on/off option;</li>
<li>template override on/off option;</li>
<li>documentation links for each tag.</li>
</ul>
Shortcode
[poly ELEMENT-TAG ELEMENT-OPTIONS]
Tags: core-icon, paper-button, paper-checkbox, paper-slider, etc.
Options: style, id, class, etc.
Examples
<pre><code>[poly core-icon icon="favorite"][/poly]
[poly paper-checkbox][/poly]
[poly paper-button raised style="color: green"]A green button[/poly]
[poly paper-item icon="home" label="Test link"]<a href="http://www.google.it" target="_blank"></a>[/poly]
</code></pre>
Notes
<ul>
<li>code blocks allows to create elements and import them directly from the Polymer box in posts / pages. They allows also to load JSON data, see FAQ for an example</li>
<li>autop option: the autop() WordPress function adds p and br tags to the contents when a newline is found, but this can break the Polymer tags. This option allows to enable/disable autop() in posts / pages (plugin default: no autop)</li>
<li>template override option: if this option is enabled this plugin will load a special template which provides only the required components to run a Polymer app. This is useful if you want a “fullscreen” Polymer app</li>
<li>to create RESTful apps try JSON REST API (WP API) plugin. See FAQ for an example</li>
</ul>

Polymer for WordPress

John James Jacoby

Andrew Norcross

Matthew Gerring

This plugin adds a simple post-type drop-down to the post editor interface, allowing you to reassign any post to a new post type. It allows you to switch post’s type while editing your post.
<h4>Supported Types</h4>
The plugin can convert nearly every combination of posts, pages, and even custom post types:
<ul>
<li>Page to Post</li>
<li>Post to Page</li>
<li>Post to Custom</li>
<li>Custom to Custom</li>
</ul>
As of 3.0.0, support for switching to or from Attachments was removed. This may come back in a subsequent version.
Invisible post types, such as revisions, menus, etc., are purposely excluded. But, if you need to access invisible post types, you can adjust the boundaries using the ‘pts_post_type_filter’ filter.
<h4>Bulk Editing</h4>
With bulk editing (thanks to Matthew Gerring) you can select all the posts in a certain type and convert them to a new type with one quick action.
<h4>Block Editor</h4>
With block-editor (aka Gutenberg) support (thanks to Daniel Bachhuber) you can switch between post-types that use either the Block Editor and the Classic one, without losing any of your embedded content.

Post Type Switcher

Absolutely excellent


Post Type Switcher is a fantastic tool for quickly and easily changing the post type of posts and pages. Its simplicity is its strength—no unnecessary complications, just a straightforward solution that works seamlessly. Whether you're reorganizing your content or fixing mistakes, this plugin saves time and effort. Highly recommended for anyone managing WordPress content!


A Simple Yet Incredibly Useful Plugin

A simple way to change a post's type in WordPress

Polymer for WordPress vs Post Type Switcher