The North Face and Etsy Inc. improved their mobile home page load times the most on the Internet Retailer Mobile Performance Index for the month of April after removing heavy media files.

The April index monitored Internet Retailer’s Top 100 retailers’ mobile home pages April 10-23, according to data provided by digital performance analytics company Catchpoint Systems Inc. Catchpoint provides Internet Retailer with two monthly site performance indexes: one for mobile sites and one for desktop sites.

The North Face (part of VF Corp., No. 91 in the Internet Retailer 2017 Top 1000) rocketed 68 positions up the index to No. 23 from No. 91 last month. The paged loaded in a quick 2.13 seconds on average in April compared with 5.49 seconds in on average in March. The culprit for March’s slow load time was a heavy video file—almost 4 megabytes—that delayed the load time, a Catchpoint spokesman says.

“The load time improved drastically when this video was replaced with a smaller file—less than 1 megabyte,” he says.

Similarly, marketplace Etsy (No. 22) improved its web page load time to 1.85 seconds from 2.30 seconds, which moved it up to No. 15 this month from No. 27.  Etsy’s mobile site speed suffered from a few MP4 media files that bloated the page, the Catchpoint spokesman says. Once those were removed, the mobile site became significantly faster, he says. Etsy declined to comment.

Heavy page elements, however, don’t have to slow a mobile home page. A good example of this is Restoration Hardware (No. 51), which has a 14.5-megabyte mobile home page (the index average is 2.26 megabytes), yet loaded in 3.51 seconds on average in April, which is only slightly longer than the index average of 3.31 seconds.

Restoration Hardware’s mobile page loaded quickly thanks to its optimized page structure, Catchpoint says. The page first downloads scripts, then images, then third-party content, or content provided by another source, Catchpoint says. Plus the site has a low number of hosts, 21, compared with the index average of 45. Hosts are domains that deliver data, content or service over the internet to the site.

For the two weeks of April 10-23, the Top 100 retailers’ average load time was 3.31 seconds compared with 3.54 the previous month. The average page weight was 2.25 megabytes compared with 2.73 megabytes the previous month, and the average number of hosts was 45 compared with 47. The average number of items was 166 compared with 168 a month ago.

The 100 sites were, on average, 99.83% available for April 10-23 compared with 99.94% available for March 27-April 9. These are the 100 leading North American retail sites by online sales for 2015, according to Top500Guide.com.

Catchpoint monitors each website’s home page with measurements taken from Catchpoint’s in-country or in-region monitoring nodes, at intervals of five minutes for two weeks each month. Backbone monitoring nodes are the locations of Catchpoint’s devices that are near data centers operated by the main internet service providers that provide service to a city. The nodes simulate end-user contact with each website. Catchpoint monitors webpage load time, availability, hosts and items.

They are defined as follows:

Web page load time: The time it takes for enough page elements to load for a consumer to begin interacting with a page, such as searching, tapping or scrolling. From a consumer point of view, the time it takes for the progress bar or spinning wheel to stop.

Availability: The percentage of time during the two-week test week that the site can be successfully reached by a consumer.

Host: Any domain that delivers data, content or services over the internet to the site.

Items or Requests: Web page components, such as files or images that a page loads from internal and external hosts or domains. These can include PDFs, PNGs, JPEGs and GIFs.