Rope, 3/8", 1000 feet
Hollow Braid Monofilament Polypropylene, Yellow

IMPORTANT NOTE
Don't purchase rope based on the "size" or diameter.  Instead, buy rope based on the specifications below.  Rope from different manufacturers will have different "actual diameter" and, more importantly, different specifications.  Instead of buying "standard 3/8 inch rope", buy rope using the specifications below.

Breaking Strength: 1800 lbs
Price is for 1000 feet (305 m)
Weight of 1000 foot spool (in box): 22 Lbs

Minimum Glider Weight (200% rule): 900 Lbs 
Maximum Glider Weight (80% rule): 2250 Lbs

Dimensions of shipping box: 13 x 13 x 16 inches

Minnesota Soaring Club Rope Tips Document - Excellent!!!
https://mnsoaringclub.com/wp-content/uploads/2021/03/TowropeProof1.pdf

U.S. Towrope Regulations
FAR Part 91, section 91.309 states:

(3) The towline used has breaking strength not less than 80 percent of the maximum certificated operating weight of the glider or unpowered ultralight vehicle and not more than twice this operating weight. However, the towline used may have a breaking strength more than twice the maximum certificated operating weight of the glider or unpowered ultralight vehicle if - 

(i) A safety link is installed at the point of attachment of the towline to the glider or unpowered ultralight vehicle with a breaking strength not less than 80 percent of the maximum certificated operating weight of the glider or unpowered ultralight vehicle and not greater than twice this operating weight; 
(ii) A safety link is installed at the point of attachment of the towline to the towing aircraft with a breaking strength greater, but not more than 25 percent greater, than that of the safety link at the towed glider or unpowered ultralight vehicle end of the towline and not greater than twice the maximum certificated operating weight of the glider or unpowered ultralight vehicle;