There are only three 20" wheel or smaller suspension forks on folding bikes. These are found on the Dahon Jetstream, Birdy, and Downtube. We will examine all three.

The Dahon fork is super light. It is essentially a rear shock connected to a fork. It performs well, however it main utility is to stay light....it's not supposed to add too much comfort. Overall bit is a good fork that costs a small fortune to purchase. I recall they costed $400+ many years ago. I'm scared to ask the current cost, but I guess it's over $700.

The Birdy fork allows for a super compact fold. It is a brilliant design that is light and small. However the suspension is not ideal. It takes the edge off of bumps. However that is all. Overall I love Birdy's. I just wish the suspension was more forgiving.

Downtube uses forks from HL Corporation. They own the Zoom brand, and produce a large percentage of the global supply of suspension forks, stems, and seatposts. These forks are the heaviest 29" wheel forks, so they are not light. However they are cost effective ( under $100 retail ). They are preload adjustable and comfy.

Overall all folding bike suspension forks are good. Pick the one that suits your needs.