Cochrane review of foam dressings for healing diabetic foot ulcers concludes:
"We found no evidence that foam dressings promote the healing of diabetic foot ulcer compared with basic wound contact dressings. When data from two studies (eight and 12 weeks follow-up) were pooled, there was no statistically significant difference in ulcer healing between alginate and foam dressings. Similarly there was no evidence of a difference in the number of diabetic foot ulcers healed between foam and hydrocolloid (matrix) dressings. We note that most included studies were evaluating treatments on participants with non-complex foot ulcers. This means the body of literature presented may be of limited use to health professional in the treatment of patients with harder to heal foot ulcers as it is difficult to generalise from the included studies to patients with more co-morbidities or complications; this is a limitation of the RCTs that have been undertaken in this field thus far. Included trials were small and therefore statistically underpowered to detect important treatment differences should they exist." 
No evidence of clinical benefit from foam dressings and generally poor quality studies. This is a good reminder that it is not often about what you "put on" the ulcer but what pressure you "take off".
1. Dumville JC, Deshpande S, O’Meara S, Speak K. Foam dressings for healing diabetic foot ulcers. Cochrane Database Syst Rev 2011;9:CD009111. Available from: http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD009111.pub2/full